PRECIOUS    STONES 


BY 


W.     GOODCHILD    M.B.    Ch.B. 
v 


WITH   A    CHAPTER    ON 
ARTIFICIAL     STONES 

BY 

ROBERT    DYKES 


NEW    YORK 

D.    VAN    NOSTRAND    COMPANY 
23    MURRAY   AND    27    WARREN    STREETS 

1908 


v\ 


GENERAL 


BKADBURY,    AGNEW,    &    CO.    I.D.,    PRINTKR! 
LONDON   AND   TONBRJDGE. 


PREFACE 

THE  author  has  to  acknowledge  his  indebtedness  to  E.  C. 
Munro  Ferguson,  Esq.,  M.P.,  for  permission  to  figure  some 
of  the  very  fine  specimens  of  Precious  Stones  contained  in 
the  Eaith  Collection  ;  to  Dr.  J.  B.  Hears,  of  Edinburgh, 
for  his  careful  drawings  and  photographs  of  these  speci- 
mens ;  to  Mr.  E.  Dykes,  of  the  Marine  Biological 
Laboratory,  Lowestoft,  and  lately  assistant  to  Sir  J. 
Murray,  K.C.B.,  for  his  chapter  on  the  artificial  production 
of  Precious  Stones ;  and  to  the  life-teaching  of  his  late 
father,  J.  G.  Goodchild,  of  H.M.  Geological  Survey. 
Among  the  numerous  larger  works  on  this  subject  the 
reader  is  especially  referred  to  the  splendid  book  by 
Dr.  Max  Bauer,  translated  by  Mr.  L.  J.  Spencer,  of  the 
British  Museum. 

The  different  gem  stones  are  here  considered  in  a 
mineralogical  sequence,  and  the  numbers  preceding  the 
names  are  the  species  numbers  of  Dana's  System. 


WILBEET   GOODCHILD. 


THRELKELD, 

October,  1907. 


207104 


CONTENTS 


CHAP. 

I.  INTRODUCTORY   AND    HISTORICAL         ....            1 

II.       MODES   OF   ORIGIN 7 

III.  THE    PHYSICAL    PROPERTIES   OF  GEM   STONES      .            .         21 

'      IV.       THE   CUTTING    OF   GEMS 50 

V.  IMITATION   GEMS   AND   THE    ARTIFICIAL    PRODUCTION 

OF   PRECIOUS    STONES    .  .  .  .  .  .67 

VI.       THE   DIAMOND 98 

VII.  FLUOR    SPAR — OPAL             .            .            .                                    .       141 

VIII.       CORUNDUM 183 

IX.  SPINEL    AND   CHRYSOBERYL         .            .            .            .            .198 

X.  CALCITE — LABRADORITE    .            .            .                        .            .       205 

XI.  AUGITE — CROCIDOLITE       .            .            .            .            .            .218 

XII.       BERYL— GARNET 228 

XIII.      OLIVINE — SPHENE 253 

XIV.  APATITE — JET                                                                                            283 


GLOSSARY .291 

INDEX  •       299 


LIST     OF     ILLUSTRATIONS. 

FIG.  PACK 

1.  DIAGRAM   OF   REFRACTION 23 

2.  DIAGRAM   OF   DISPERSION 24 

3.  REFRACTION   AND   INTERNAL   REFLECTION     .  ,  .25 

4.  THE   TABLE 52 

5.  STEP-CUT 52 

6.  THE   ROSE 52 

7.  BRILLIANT-CUT 52 

8.  THE    PITT   OR   REGENT   DIAMOND  ....         52 

9.  DIAMOND  :     A   NATURAL   CRYSTAL  .  .  .  .99 

10.  DRAWINGS    OF   CRYSTALS    OF   DIAMOND  .  .  .100 

11.  DRAWINGS   OF   CRYSTALS    OF   DIAMOND  .  .  .101 

12.  QUARTZ  :   VAR.    ROCK   CRYSTAL.       FROM   DAUPHINF,          .       148 

13.  QUARTZ:    VAR.       VENUS'   HAIR    STONE.  .  .  .158 

14.  CORUNDUM 186 

15.  SPINEL •  .  .  .  .       199 

16.  ADULARIA  . 211 

17.  DIOPSIDE .219 

18.  CRYSTAL  OF  BERYL 230 

19.  CRYSTAL  OF  BERYL 230 

20.  EMERALD  IN  ITS  MATRIX 231 

21.  EMERALD  IN  THE  MATRIX  (COLOMBIA)    .     .     .233 

22.  BERYL  CRYSTALS,  PARTLY  COATED  WITH  LIMONITE  .   236 

23.  GARNET   .     .- 244 

24.  GARNET '.     .   244 

25.  GARNET  CRYSTALS  IN  THE  MATRIX  ....   246 
P.S.  b 


x  LIST  OF  ILLUSTRATIONS. 

FIG.  -                                                                                                                                                                                               PAGE 

26.  A  GROUP  OP  GARNET  CRYSTALS     .     .     .     .   247 

27.  GARNET  WITH  ALALITE 248 

28.  OLIVINE 253 

29.  DIOPTASE 256 

30.  IDOCRASE   . 257 

31.  IDOCRASE    IN   THE   MATRIX 258 

32.  ZIRCON  :    TYPICAL   FORM 259 

33.  ZIRCON  :    UNEQUALLY   DEVELOPED   CRYSTAL  .  .259 

34.  ZIRCON,   IN   A   PEGMATITE   MATRIX         ....      260 

35.  BLUE   TOPAZ   WITH   SMOKY   QUARTZ      ....       263 

36.  TOPAZ 264 

37.  TOPAZ  :     AN   UNEQUALLY    DEVELOPED   CRYSTAL      .  .       265 

38.  A    GROUP   OF   AXINITE    CRYSTALS  ....       272 

39.  CHARACTERISTIC   FORM   OF   TOURMALINE       .  .  .275 

40.  TOURMALINE   IN   THE    MATRIX 276 

41.  PRECIOUS   SERPENTINE    (POLISHED)       ....       280 

42.  GYPSUM  ;    VARIETY   SATIN   SPAR  .  .  .  .287 


OF  THE 

UNIVERSITY 


PRECIOUS   STONES. 


CHAPTER  I. 

INTEODUCTOEY    AND    HISTOEICAL. 

FROM  the  earliest  times  gems  and  precious  stones  have 
been  prized  on  account  of  their  beauty  and  for  the  purposes 
of  personal  adornment ;  this  is  amply  shown  by  the 
numerous  references  to  them  by  the  ancient  authors ;  Pliny, 
in  Books  XXXVI.  and  XXXVII.  of  the  Natural  History, 
quotes  from  many  of  these  works,  all  of  which,  except  that 
of  Theophrastus,  are  now  lost.  A  considerable  number  of 
these  writers  were  Greeks,  and  several  of  them  would 
appear  to  have  lived  in  or  visited  more  Eastern  lands, 
where  very  probably  their  interest  in  the  precious  stones  was 
largely  brought  into  being.  King,  in  his  work  on  "  The 
Natural  History  of  Precious  Stones,"  calls  attention  to 
the  fact  that  Socatus,  one  of  the  authors  quoted  by  Pliny, 
speaks  of  having  seen  a  certain  wonderful  gem  in  the 
possession  of  the  King,  which  according  to  Greek  usage 
would  mean  the  king  of  Persia ;  this  gives  us  a  definite  con- 
ception of  the  antiquity  of  this  love  of  gems.  Another 
author  quoted  by  Pliny  is  spoken  of  as  Zachalias  the 
Babylonian — again  pointing  to  the  connection  between  the 
study  of  this  subject  and  the  ancient  civilisation  of  the 
East.  This  relation  may  be  accounted  for  by  the  fact  that 
p.s.  B 


2  PEEOIOUS   STONES. 

many  of  the  earliest  known  localities  for  gems  were  in  the 
East,  or  on  the  other  hand  it  may  be  that  the  people  of  the 
lands  to  the  north-west  of  India  first  showed  a  marked 
degree  of  civilisation  and  hence  first  observed  these  wonders 
of  Nature,  and  sought  for  and  found  new  localities  where 
they  occurred. 

In  these  early  times  gems  were  prized  not  only  for  orna- 
ment but,  possibly  to  an  even  greater  extent,  for  supposed 
magical  and  medicinal  virtues^magic  and  medicine  being 
then  only  too  closely  associated.  Under  the  accurate  learn- 
ing of  the  best  period  of  Greek  civilisation  there  seems  to 
have  been  a  much  larger  amount  of  scientific  observation 
brought  to  bear  on  the  subject.  Pliny  in  his  time  showed 
a  still  greater  exactness,  and  moreover  a  marked  contempt 
for  the  "  preposterous  lies  of  the  impudent  Magi."  Solinus, 
a  Koman  writer  probably  'of  the  period  of  Constantine, 
improves  further  on  some  of  Pliny's  descriptions  of  gems. 

Later  again,  the  seemingly  very  deep-rooted  belief  in  the 
medicinal  properties  of  gems  coloured  a  great  part  of 
another  work ;  this  was  the  "  Origines "  of  Isidorus  of 
Seville,  written  in  the  seventh  century.  The  book,  however, 
is  valuable  in  containing  quotations  from  writings  now  lost. 
Isidorus  was  a  bishop,  and  one  of  the  next  works  of  which 
we  have  record  was  also  the  writing  of  a  bishop — Marbodus, 
bishop  of  Kennes.  Marbodus  says  his  work  is  a  con- 
densation of  that  of  Evax,  King  of  Arabia ;  King,  however 
(op.  cit.),  is  of  the  opinion  that  no  such  book  was  written 
by  Evax,  but  that  it  was  a  compilation  made  after  the  period 
of  truer  learning.  Both  these  books  show  a  retrograde 
step,  in  going  back  to  the  mystical  rather  than  in  advancing 
the  scientific  knowledge  of  the  subject. 


PEECIOUS  STONES.  3 

In  the  twelfth  century  a  "  Book  on  Precious  Stones"  was 
written  by  Mohammed  Ben  Mansur,  of  great  value  on 
account  of  it  being  of  a  much  more  exact  nature  than  any 
of  its  forerunners,  though  much  of  his  information  would 
appear  to  have  been  derived  from  the  same  source.  In 
spite  of  the  forward  step  which  the  appearance  of  this  work 
marks,  it  was  followed  by  a  number  of  other  books  which, 
from  the  point  of  view  of  the  present  day  mineralogist, 
entirely  forsook  the  subject,  as  they  dealt  almost  wholly 
with  the  supernatural,  ascribing  to  gem  stones  all  sorts  of 
powers  against  evil  spirits,  diseases,  and  the  mighty  mani- 
festations of  Nature.  These  ideas  were  still  further  modified 
by  a  growth  in  the  belief  that  various  symbols  and  inscrip- 
tions engraved  on  the  stones  were  able  to  enhance  their 
already  supernatural  powers.  King  (op.  cit.)  ascribes  these 
new  forms  of  thought  to  the  influence  of  the  Crusades  upon 
the  learning  of  the  country,  in  bringing  back  magic-lore 
gleaned  from  the  Arabic  philosophers. 

No  further  work  of  any  great  value  appeared  till  that  of 
Boetius  de  Boot,  physician  to  the  Emperor  Kudolf  II., 
which  was  entitled  "  De  Gemmis  et  Lapidibus,"  and  which 
was  published  in  1609.  At  the  same  time  De  Boot,  while 
decrying  the  magical  powers  ascribed  to  gems,  goes  on  to 
give  recipes  for  the  making  of  various  pharmacopoeial  pre- 
parations of  precious  stones.  In  1672.  again,  we  find  Eobert 
Boyle,  one  of  the  early  Fellows  of  the  Eoyal  Society,  in  his 
''Essay  About  the  Origin  and  Virtues  of  Gems,"  after 
making  most  careful  reservations  in  his  preface  as  to  what 
his  opinions  were  about  the  virtues  of  gems,  and  stating 
that  "  not  only  some  of  the  writers  of  Natural  Magick,  but 
men  of  note,  who  should  be  more  cautious  and  sober,  have 

B2 


4  PKECIOUS   STONES. 

delivered  in  their  Writings  many  things  concerning  Gems, 
which  are  so  unfit  to  be  credited,  and  some  of  them  perhaps 
so  impossible  to  be  true,  that  I  hope  the  Believers  of  them 
will,  among  the  Votaries  to  Philosophy,  be  as  great  rarities 
as  Gems  themselves  are  among  Stones,"  going  on  to 
seriously  make  the  following  statement :  "  And  we  see,  that 
soft  Stone,  which  is  plentifully  found  near  Naples,  and 
commonly  call'd  the  Lapis  Lyncarius,  being  rubb'd  a  little 
and  moistened  with  water,  and  then  expos'd  to  the  Sun  in 
a  due  season  of  the  year,  will,  in  a  very  short  time,  (as  Eye- 
witnesses have  assured  me,)  produce  Mushrooms  fit  to  be 
eaten."  The  Lapis  Lyncurius  was  either  Amber,  or  more 
probably,  as  suggested  by  Sir  J.  Hill,  Hyacinth,  a  variety 
of  Zircon — not  at  all  a  good  germinating  ground  for  the 
spores  of  mushrooms.  And  again  he  says,  "  because  I 
find  no  impossibility  that  at  least  some  costly  and  less  hard 
(though  indeed  more  valuable)  Gems,  may  have  consider- 
able operations  upon  humane  Bodies,  some  few  of  which  I 
have  had  opportunity  to  be  convinc'd  of,  I  will  not  indiscrimi- 
nately reject  all  the  Medicinal  Virtues  that  Tradition  and 
the  Writers  about  pretious  stones  have  ascribed  to  those 
Noble  Minerals."  Still,  Boyle's  book  is  most  fascinating, 
and  shows  he  was  an  active  champion  of  the  hypothesis  of 
the  aqueous  origin  of  most  minerals,  a  cause  which  Gustav 
Bischof,  nearly  two  centuries  later,  again  felt  the  need  of 
impressing  on  the  scientific  world  in  opposition  to  the 
Plutonic  theory  of  the  origin  of  all  minerals  and  rocks. 

In  dealing  with  the  properties  anciently  ascribed  to  gems 
and  precious  stones,  it  is  necessary  to  point  out  that  the  old 
conceptions  as  to  what  was  included  in  these  two  classes 
were  very  different  from  those  of  the  present  day.  By  "  gem ' ' 


PEECIOUS  STONES.  5 

we  now  understand  a  mineral  which  by  its  hardness,  rarity, 
lustre  or  colour  is  used  for  the  purposes  of  adornment ;  a 
precious  stone  is  also  usually  a  mineral,  and  possesses  these 
same  qualities  in  a  minor  degree.  Most  of  the  true  gem 
stones  are  crystallised  and  are  transparent  or  at  least 
translucent.  Formerly,  however,  besides  including  all  the 
then  known  stones  that  fell  under  the  above  heads,  many 
substances  were  regarded  as  precious  stones  which  were  of 
a  very  different  origin,  and  that  often  for  very  different 
reasons  than  on  account  of  their  beauty.  Fossils,  for  instance, 
were  at  one  time  held  in  high  esteem  in.  this  relation  and 
were  accredited  with  great  use  in  the  preparation  of  medicinal 
remedies,  and  that  apparently  chiefly  on  account  of  their 
peculiar  shapes.  Again,  we  find  that  when  glass  was  scarce 
a  cup  of  that  material  was  considered  fit  to  rank  with 
ornaments  made  from  what  we  still  regard  as  precious 
stones. 

The  individual  properties  ascribed  to  the  various  stones 
will  be  noticed  in  the  part  dealing  with  each  substance,  but 
a  few  general  examples  may  be  given  here  to  illustrate  the 
point.  The  Diamond,  for  instance  (though  not  known  to  the 
earliest  writers),  is  frequently  referred  to  on  account  of  some 
of  the  following  reputed  properties  :  taken  internally  it  is  a 
violent  poison — it  is  said  to  have  been  administered  to  Sir 
T.  Overbury  (amongst  other  poisons)  when  a  prisoner 
in  the  Tower — and  yet  Garcias  records  a  case  that  came 
under  his  notice  of  a  woman  giving  her  husband  repeated 
doses  of  diamond-dust  to  relieve  dysentery,  but  without 
effect ;  the  physician  Camillo  Leonardo  in  the  sixteenth 
century  declares  it  is  a  poison  of  a  most  violent  kind,  and 
Cellini  tells  how  an  enemy  tried  to  poison  him  by  employing 


6  PEECIOUS  STONES. 

an  apothecary  to  place  powdered  Diamond  in  his  salad, 
but  was  saved  by  the  apothecary  substituting  some 
powdered  Beryl.  Truth  is  probably  with  both  sides  :  an 
unbroken  Diamond  can  be  swallowed  by  a  Kaffir  with 
intent  to  steal  without  harm  to  his  system,  but  sharp  frag- 
ments of  Diamond  would  be  as  much  an  irritant  poison  as 
powdered  glass  in  the  same  quantity.  Diamond,  again, 
dispels  unfounded  fear,  and  is  a  protection  against  insanity; 
and  Boyle  (op.  cit.)  instances  a  quaint  belief  in  the  follow- 
ing words:  "  If  it  happen  that  the  Mineral  Corpuscles,  that 
are  wont  to  impart  a  certain  Virtue  to  the  stony  matter  of 
one  Gem,  should,  by  some  lucky  hit,  be  so  united  with  that 
of  another  sort  of  Gems  (of  which  case  I  formerly  gave  an 
Instance  in  green  Diamonds,)  though  the  quantity  of  this 
unusual  Ingredient  may  be  but  very  small,  yet,  if  it's 
efficacy  be  great,  it  may  innoble  the  Stone  with  a  notable 
degree  of  some  such  Virtue  as  is  supposed  not  to  belong  to 
that  Species,  but  to  an  other." 


CHAPTEK  II. 

MODES    OF    ORIGIN. 

THE  origin  of  each  gem  will  be  dealt  with  in  its  proper 
place,  but  here  again  a  few  general  points  may  be  noticed. 
It  is  well  worth  the  reader's  while  to  study  such  a  book  as 
that  of  Kobert  Boyle's  above  referred  to,  to  gain  an  insight 
into  the  earnest  endeavours  these  old  scientists  made  to  dis- 
cover the  how,  why,  and  wherefore  of  Nature's  working. 
Aristotle  in  the  third  book  of  Meteors  states  his  belief  that 
the  infusible  stones  were  made  by  a  "  dry  exhalation  " ; 
another  theory  was  that  they  were  formed  of  a  mixture  of 
earth  and  water  congealed  by  cold ;  later  again  the  almost 
universal  belief  was  that  they  originated  from  the  actual 
fusion  by  heat  of  various  earthy  matters.  Boyle,  by  careful 
"  examens  "  of  different  chemical  substances,  as  alum,  salt, 
saltpetre,  etc.,  in  the  process  of  crystallisation,  came  to  the 
conclusion  that  all  gems  originated  from  crystallisation 
from  a  watery  solution  ;  he  came  to  the  conclusion  that 
for  the  particles,  of  which  the  mineral  was  composed,  to 
be  able  to  move  into  their  proper  places  so  as  to  unerringly 
build  up  a  crystal  of  a  definite  geometrical  form,  these 
particles  must  have  existed  in  a  fluid  state  of  some  sort. 
Crystals  are  formed  either  by  sublimation,  solidification 
from  a  molten  mass,  or  separation  from  a  solution,  and  it 
is  quite  possible  one  of  the  commonest  ways  of  formation 
of  the  crystals  of  mineral  substances  is  by  separation  from 


8  PEECIOUS  STONES. 

a  solution  at  a  great  temperature  and  under  enormous 
pressure.  Suppose  we  dissolve  in  cold  water  as  much 
Glauber's  salts  (sodium  sulphate)  as  possible  and  then  heat 
the  solution  to  nearly  the  boiling  point,  on  adding  more  of 
the  salt  we  shall  find  it  dissolve  readily,  and  conversely  on 
cooling  it  will  be  again  deposited  in  a  visible  form  as 
crystals.  In  such  a  case  the  temperature  to  which  we  can 
raise  the  solution  is  very  nearly  fixed  by  the  pressure  of  the 
atmosphere  ;  if,  however,  we  heated  the  solution  in  a  strong 
metal  vessel  capable  of  withstanding  a  pressure  of  several 
hundred  pounds  to  the  square  inch,  we  should  find  that 
crystals  of  the  Glauber's  salts  which  remained  undissolved 
at  the  ordinary  boiling  point  were  dissolved.  Thus  we  can 
reason  that  given  sufficient  heat  and  sufficient  pressure  and 
sufficient  time,  many  substances,  which  in  the  chemical 
laboratory  seem  insoluble,  may  be  readily  dissolved.  Con- 
versely on  the  lowering  of  the  temperature  and  the  relief 
of  the  pressure,  it  is  possible  to  have  such  mineral  substances 
deposited  from  solution ;  in  other  words,  they  may  appear 
as  crystals.  It  is  more  than  probable  that  some  gems  are 
actually  deposited  as  crystals  from  a  molten  magma,  but  it 
is  even  more  certain  that  some  are  formed  on  the  cooling 
of  solutions  at  high  temperatures. 

While  most  precious  stones  are  crystalline,  some  few,  as 
the  Opal,  are  probably  not,  but  the  distinction  is  now 
regarded  as  a  somewhat  arbitrary  one ;  whether  crystalline 
or  colloid,  Opal  is  probably  deposited  by  water  charged  with 
silica  slowly  percolating  through  fissures  in  rocks. 

In  dealing  with  the  origin  of  the  various  gems,  the  classi- 
fication proposed  by  J.  G.  Goodchild '  will  be  followed  in  the 

1  "  Proc.  Eoyal  Physical  Soc.,"  vol.  xiv.,  p.  183. 


PKECIOUS   STONES.  9 

main,  for  though  it  was  put  forward  chiefly  in  connection 
with  certain  Scottish  minerals,  it  covers  most,  if  not  all, 
of  the  minerals  with  which  we  have  to  deal,  since  the 
majority  fall  under  comparatively  few  heads  which  will  be 
dealt  with  fully  as  being  more  important  to  our  purpose  :— 

I.  Epigene  minerals. 

Aj. — Those  whose  first  stages  consist  in  their  being 
dissolved  at  the  surface,  and  then  re-deposited 
elsewhere  outside  the  lithosphere. 

(a)  Those  deposited  on  the  land. 

(b)  ,,  ,,  in  fresh  water. 

(c)  ,,  ,,  in  closed  bodies  of  water. 

(d)  „            „  at  the  bottom  of  the  sea. 
A2. — Those  whose  materials  arise  through  solution 

at  the  surface,  and  subsequent  re-deposition 
within  the  lithosphere. 

A3. — Those  due  to  subterranean  percolation  of  waters 
from  the  surface. 

(a)  Those  which  are  altered  in  situ. 

(b)  Those    whose     materials     have    been 

dissolved  within  the  lithosphere,  and 
subsequently  re-deposited  at  lower 
levels. 

II.  Hypogene  minerals.     Mostly  of  hydro-thermal  origin, 
and   usually   connected   with   some   manifestation   of 
elevatory  movement. 

B!. — Original  minerals  of  eruptive  rocks. 

(a)  Silicates. 

(b)  Metals  and  their  compounds. 

(c)  Other  minerals. 

B2. — Original  contents  of  mineral  veins. 


10  PKECIOUS  STONES. 

B3. — Minerals  arising  from  solfataric  action. 

64. — Those   deposited    at    the   surface   by   thermal 
springs. 

B5. — Those  arising  through  thermo-metamorphism. 

Be- — Minerals     arising     through     dynamic     meta- 
morphism. 

B7. — Combinations  of  the  effects  of  B5  with  those  of 

B6. 

Under  Ai  we  are  only  immediately  concerned  with  some 
forms  of  Gypsum,  which  come  under  (c).  During  past 
geological  times  there  were  in  some  areas  great  closed  lakes 
similar  to  the  Dead  Sea  at  the  present  time ;  the  rivers 
flowing  into  these  brought  down  many  salts  in  more  or  less 
dilute  solution;  now  it  is  at  once  obvious  that  if  a  lake 
persists  with  no  outlet,  the  evaporation  from  its  surface 
must  be  sufficient  to  account  for  all  the  water  brought  to 
the  lake  by  the  rivers  flowing  into  it  (with  the  exception  of 
a  small  quantity  which  may  intrude  into  the  surrounding 
rocks).  Thus,  as  the  water  evaporates  the  solution  of  the 
various  salts  is  concentrated,  and  some  of  the  salts  finally 
deposited.  The  Gypsum  probably  results  from  the  double 
decomposition  of  magnesium  sulphate  and  calcium  hydro- 
gen carbonate,  both  contained  in  the  water.  It  may  also 
arise  by  the  concentration  of  estuarine  or  brackish  water  in 
shallow  lagoons.  Once  it  is  disseminated  in  scales  through- 
out the  mud  at  the  bottom  of  the  lake,  we  can  more  easily 
account  for  the  subsequent  segregation  into  masses  which 
has  occurred  in  most  known  gypsum-beds ;  such  segregation 
would  come  under  the  head  A3  (b). 

The  next  group  we  are  concerned  with  is  A3  (a)  dealing 
with  those  minerals  which  have  been  produced  by  alteration 


PRECIOUS  STONES.  11 

of  pre-existing  minerals  in  situ:  take  Serpentine  as  an 
example  ;  it  is  a  silicate  of  magnesium  (often  with  some 
iron  replacing  part  of  the  magnesium)  with  some  water, 
which  water  is  only  driven  off  at  a  red  heat,  and  is,  there- 
fore, in  chemical  combination.  Now,  there  is  in  nature  a 
very  large  number  of  ferro-magnesian  silicates,  and  several 
of  these,  when  acted  on  by  downward  percolating  water 
(probably  containing  small  quantities  of  alkaline  carbonates 
in  solution,  imd  certainly  acting  over  long  periods  of  time), 
are  hydrated,  and  one  of  the  substances  that  may  be  so 
formed  is  Serpentine: 

The  next  group  is  much  more  important,  as  it  includes 
some  forms  of  Calcite,  all  the  true  Agates,  and  the  minerals 
Prehnite,  Opal,  Dioptase,  Turquois,  and  many  of  the  forms 
of  Quartz  and  Chalcedony. 

Consider  these  same  waters  referred  to  above,  charged 
with  traces  of  alkaline  carbonates,  and  percolating  downward 
through,  say,  a  mass  of  ancient  lava.  First  we  may  ask, 
"  Whence  came  the  carbonate  in  solution  ?  "  Eain  falling 
on  the  earth  contains  a  certain  (small)  amount  of  carbon 
dioxide  or  carbonic  acid :  as  the  water  percolates  through 
the  layers  of  the  soil  it  becomes  further  charged  with  the 
humus  acids — allied  to  carbonic  acid,  and  generated  largely 
by  the  action  of  bacteria  upon  the  organic  matter  which  is 
everywhere  present  on  the  surface.  This  weak  acid  solution 
in  the  course  of  time  acts  on  some  of  the  constituents  of 
the  lava,  and  slowly  dissolves,  for  instance,  one  of  the 
complex  silicates  containing  sodium.  Thus  a  weak  solution 
of  sodium  carbonate  is  formed.  Such  a  solution  would 
probably  have  no  perceptible  action  on  a  piece  of  lava  in 
a  laboratory,  because  we,  relatively  speaking,  neglect  the 


12  PKECIOUS  STONES. 

all-important  factor,  time.  But  in  Nature's  laboratory  it  is 
quite  different,  and  the  rock-forming  minerals  of  the  lava 
are  slowly  decomposed,  a  small  portion  of  the  material 
being  carried  deeper  into  the  rock.  Now,  a  lava  frequently 
contains  steam  holes,  or  vapour  cavities,  and  if  the  solution 
meet*  one  such  in  its  downward  path,  it  is  carried  into  the 
cavity  by  osmosis.  Usually  the  first  solution  to  enter  is 
one  derived  from  the  attack  of  the  water  on  one  of  the  ferro- 
magnesian  minerals,  and  once  it  is  in  the  cavity  a  thin  film 
of  a  mineral  (in  most  cases  one  allied  to  Serpentine)  is 
deposited  on  the  wall  of  the  cavity,  and  forms  what  is  called 
the  "  priming."  Dr.  Heddle  showed  this  priming  to  consist 
in  most  cases  of  Celadonite.  The  thickness  of  this  layer 
may  vary  from  a  mere  film  to  one  entirely  filling  the  cavity. 
If  the  Celadonite  continued  to  be  deposited  along  with  silica 
in  the  form  of  Chalcedony,  it  often  took  the  form  of  moss- 
like  growths,  surrounded  by  the  clear  Chalcedony,  giving 
rise  thus  to  a  Moss  Agate.  If  the  Celadonite  and  Chalcedony 
were  intimately  mixed  Prase  or  Heliotrope  would  be  formed. 
Later  silica  in  solution  was  carried  into  the  cavity  by 
osmosis,  and  deposited  next  inside  the  priming,  or  only 
separated  from  the  Celadonite  by  a  thin  layer,  to  be  described 
immediately.  The  deposition  of  the  silica  took  the  form  of 
Chalcedony,  and  was  very  probably  brought  about  by  the 
escape  of  the  solvent.  Often  the  decomposition  of  the  ferro- 
magnesian  silicates  was  closely  followed  by  the  disintegra- 
tion of  the  felspars  of  the  rock,  and  the  resulting  products 
carried  into  the  cavity  and  deposited  immediately  within 
the  Celadonite,  as  a  layer  of  one  of  the  Zeolites.  Earely  the 
entire  cavity  might  be  filled  with  Zeolite.  All  three  of  these 
minerals  form  coatings  of  practically  uniform  thickness. 


PEECIOUS  STONES.  13 

In  other  words,  the  roof  received  as  much  deposition  as 
the  floor.  This  points  to  a  considerable  degree  of  surface 
tension  between  the  solution  of  silica  and  the  pre-formed 
portion  of  the  Agate ;  but  if  the  layer  of  clear  Chalcedony 
became  thick,  gravity  in  some  cases  overcame  the  surface 
tension, and  the  newly  deposited  jelly-like  silica  sagged  some- 
what, and  as  further  layers  were  added  the  sagging  would 
become  more  marked,  until  a  diminutive  stalactite  was 
formed.  The  presence  of  such  a  stalactite  increased  the 
surface  tension  at  that  point,  and  caused  a  greater  relative 
deposition  of  new  silica.  In  most  cases  small  growths  of 
zeolitic  minerals  occurred  on  the  "  skin,"  often  in  the  form 
of  minute  sheaves  of  crystals ;  thus  at  such  points  the 
surface  area  was  much  increased,  and  hence  also  the 
absolute  surface  tension,  leading  to  an  extra  deposit  of 
silica  there  in  layers  concentric  to  these  little  sheaves.  In 
this  manner  were  formed  the  "  eyes  "  so  commonly  seen  in 
Agates.  Where  the  eyes  were  close  together  the  bands 
took  on  the  form  of  salient  and  re-entering  angles,  giving 
on  cross-section  a  plan  somewhat  similar  to  the  plan  of  a 
fort ;  hence  such  Agates  are  called  Fortification  Agates. 

Should  much  zeolitic  matter  be  deposited  with  the  Chal- 
cedony the  Agate  has  an  opaque  chalky  appearance  and  is 
then  known  as  Chalcedony  Cachalong.  Often  too  the 
silica  is  in  the  hydrous  colloid  form,  Opal ;  or,  again,  the 
last  formed  layers  (in  the  centre)  may  be  anhydrous  and 
they  then  take  the  form  of  Quartz,  Amethyst  or  Cairngorm. 

Now  Opal  in  its  solution  seems  to  have  a  much  weaker 
surface  tension,  and  so,  instead  of  finding  it  evenly  coating 
the  inside  of  the  cavity  we  see  that  it  is  deposited  in  horizontal 
layers ;  when  the  layers  are  parallel  Onyx  is  formed,  but 


14  PEECIOUS  STONES. 

the  term  refers  to  the  parallelism  of  the  bands  and  not  to 
their  composition,  hence  Onyx  may  consist  of  Chalcedony. 
Opal  containing  finely  divided  zeolitic  material  is  true 
Cachalong. 

That  all  these  layers  remained  in  the  form  of  a  jelly 
until  (in  most  cases,  at  any  rate)  the  cavity  was  entirely 
filled,  is  clearly  shown  in  many  Agates  by  what  Dr.  Heddle 
called  the  "  tube  of  escape."  The  contents  being 
denser,  the  osmotic  pressure  was  greater;  possibly  also 
heat  was  liberated  on  the  crystallisation  of  some  of  the 
silica  ;  at  any  rate,  the  weakest  part  of  the  skin  gave  way 
and  a  minute  pore  was  formed  through  which  some  of  the 
silica  jelly  was  forced,  the  gelatinous  layers  of  silica  near 
the  opening  being  at  the  same  time  bent  outwards. 

All  such  true  Agates  being  formed  in  closed  cavities 
assume  the  shape  of  these  spaces,  which,  since  they  are 
often  steam  cavities  in  lavas,  are  in  many  cases  lenticular, 
similar  in  form  to  the  bubbles  in  inferior  glass.  Thus  one 
of  the  means  of  recognising  an  Agate  before  it  is  cut  into 
is  its  shape. 

When  ferric  oxide  is  deposited  in  the  Chalcedony  in 
minute  particles  it  imparts  a  translucent  blood-red  or  flesh 
colour  to  the  Agate,  which  is  then  called  Carnelian. 

Some  colloid  substances  are  liable  to  a  molecular  change 
causing  them  to  pass  into  a  crystalline  form  (cf.  Eoman 
glass).  Opal  is  so  liable,  and  the  change  is  accompanied  by 
decrease  in  volume,  hence  cracks  are  formed  ;  these  cracks 
are  sometimes  penetrated  by  solutions  of  hydrous  oxide  of 
manganese,  which  is  deposited  in  dendritic  forms  :  such 
Agates  are  called  Mochas. 

Vein  Agates  are  formed  in  fissures  or  spaces  in  communi- 


PEECIOUS   STONES.  15 

cation  with  the  surface ;  in  these  cases  surface  tension  still 
has  an  important  bearing  on  the  formation,  but  osmosis  is 
probably  not  a  factor.  Frequently,  included  material  is  so 
abundant  as  to  cause  opacity  ;  in  such  cases  the  variety  of 
Chalcedony  is  known  as  Jasper. 

From  the  point  of  view  of  genesis  most  crystals  of 
Dioptase  probably  come  in  this  class,  being  the  result  of 
the  decomposition  of  copper  ores  by  downward  percolating 
water  and  subsequent  deposition  of  the  copper  as  a  hydrous 
silicate  at  a  lower  level. 

Turquois  is  another  mineral  whose  origin  is  similar, 
and  in  some  cases  Gypsum  falls  under  this  head. 

In  Class  II.,  Hypogene  minerals,  are  many  of  the  gems 
and  precious  stones.  A  consideration  of  the  origin  of  many 
of  these  minerals  carries  us  into  geologically  debatable 
ground.  Many  have  been  the  hypotheses  and  theories 
advanced  to  explain  the  formation  of  such  compounds  in 
Nature's  laboratory.  As  far  back  as  1672  Robert  Boyle 
(op.  cit.)  stoutly  maintained  that  the  gems  were  deposited 
from  a  fluid — in  most  cases  he  seems  to  have  had  a  watery 
solution  in  mind;  one  of  his  passages,  on  account  of  its 
quaintness  and  its  apt  expression  of  the  point  in  question, 
may  be  quoted:  "  But  unless  a  Concreting  stone,  or  other 
like  Body  be  either  surrounded  with,  or  in  good  part  con- 
tiguous to  a  Fluid,  'tis  not  easie  to  conceive  how  it  should 
acquire  a  Curious  Angular  and  determinate  shape.  For 
Concrescent  Bodies,  as  I  may  so  speak,  if  they  have  not 
room  enough  in  an  Ambient  Fluid  for  the  most  congruous 
ranging  of  their  parts,  cannot  cast  themselves  into  fine  and 
Eegular  shapes,  such  as  I  shall  presently  show  that  divers 
Gems  seem  to  affect;  but  the  Matter  they  consist  of  must 


16  PEECIOUS  STONES. 

conform  to  the  Figures  of  the  Cavity  that  contain  it,  and 
which  in  this  case  has  not  so  much  the  Nature  of  a  Womb, 
as  of  a  Mold.  And  so  we  see  that  Salt-Petre,  and  divers 
other  Salts,  if  the  Water,  they  were  dissolv'd  in,  be  much  too 
far  boyl'd  away  before  they  are  suffer'd  to  shoot,  will,  if  the 
Liquor  fill  the  Glass,  sometimes  coagulate  into  a  Mass, 
fashion'd  like  the  inside  of  the  containing  Vessel,  or  if  a  pretty 
quantity  of  Liquor  remain  after  the  coagulation,  that  part  of 
the  nitrous  Mass,  that  was  reduc'd  to  be  concreted  next  the 
Glass,  will  have  the  shape  of  the  Internal  surface  of  it, 
whatever  that  be ;  but  those  Christals  that  are  contiguous 
to  the  remaining  Liquor,  having  a  Fluid  Ambient  to  shoot 
in,  will  have  those  parts  of  their  Bodies,  that  are  contiguous 
to  the  Liquor,  curiously  form'd  into  such  Prismatical  shapes 
as  are  proper  to  Nitre."  It  may  be  remarked  in  passing 
that  when  Boyle  speaks  expressly  of  "determinate ' '  shapes  and 
the  prismatical  shapes  proper  to  nitre,  it  seems  as  if  he  had 
recognised  the  fact  that  a  given  compound  crystallises  in 
one  definite  shape,  although  this  has  been  denied. 

As  previously  pointed  out,  Bischof  in  1854  placed  before 
geologists  arid  physicists  a  splendid  series  of  observations 
from  which  he  deduced  the  very  important  influence  of 
water  in  the  formation  of  many  compounds  commonly 
supposed  to  result  from  the  action  of  dry  heat. 

The  view  suggested  by  J.  G.  Goodchild  in  giving  the 
present  classification,  was  one  that  had  for  some  years 
previously  been  taught  by  him  ;  for  a  full  explanation  of  it 
the  reader  must  be  referred  to  the  paper  mentioned  above  ; 
in  outline  it  is  as  follows :  If  a  large  intrusive  sheet  of 
rock  be  followed  over  a  considerable  area  of  country,  its 
character  to  the  eye  is  seen  to  change  but  little,  and  on 


PEECIOUS  STONES.  17 

chemical  analysis  its  composition  is  found  to  be  very  fairly 
uniform  ;  also  it  is  seen  that  the  older  rocks  into  which  it 
is  intrusive  are  not  pushed  aside  by  the  mass,  but  rather 
replaced  by  it — there  is  no  material  increase  of  bulk ;  in 
other  words,  no  amount  of  new  matter  corresponding  to  the 
bulk  of  the  intrusive  mass  can  have  been  introduced  unless 
an  equal  bulk  had  been  removed.  This  would  manifestly 
be  unlikely,  and  at  once  suggests  that  the  intrusive  mass 
may  be  the  result  of  some  alteration  of  the  older  rock 
masses  replaced  by  it.  The  difficulty  that  at  once  con- 
fronts one  is  that  the  composition  is  so  uniform  even  in 
passing  through  considerable  masses  of  rocks  of  entirely 
different  composition ;  but  an  average  analysis  of  the  rocks 
throughout  the  extent  of  the  intrusion  reveals  the  fact  that 
the  composition  of  the  intrusive  sheet  chiefly  differs  from 
that  of  the  surrounding  rocks  in  a  greater  proportion  of 
alkali.  The  writer  above  referred  to  suggested  the  possibility 
that  such  alkali  might  be  slowly  carried  into  the  rocks  by 
osmosis  from  the  area  of  great  terrestrial  activity  along  the 
seaward  margin  of  the  land.  Once  such  alkaline  water  is 
introduced  at  points  where  activity  is  great  and  tempera- 
ture high,  rocks  may  be  liquefied  at  a  very  much  lower 
temperature  than  that  of  ordinary  dry  fusion,  so  the  depth 
and  temperature  demanded  need  not  necessarily  be  very 
great.  Most  rock-forming  minerals  have  a  fairly  definite 
melting  point,  but  of  course  different  minerals  melt  at 
different  temperatures ;  so  it  is  quite  possible  that  conditions 
might  obtain  which  would  suffice  to  introduce  into  a  rock 
that  was  on  the  whole  in  a  solid  state,  certain  minerals 
in  a  state  from  which  they  could  crystallise.  In  this  way 
a  shale  may  be  converted  into  Lydian  Htone,  and  the 
p.s.  C 


18  PKECIOUS   STONES. 

components  of  an  impure  limestone  or  other  sedimentary 
rock  may  be  rearranged  so  that  Zircon  or  Sphene  may  be 
formed,  amongst  many  other  minerals. 

Under  B2,  practically  the  only  minerals  which  concern  us 
are  Fluor  Spar  and  Quartz ;  in  a  mineral  vein  both  these  may 
result  from  the  cooling  of  heated  waters  rising  up  through 
the  great  fault-fissures.  It  may  be  noted  that  the  sequence 
of  deposition  of  these  minerals  is  usually  constant  in  any 
given  vein,  and  that  such  sequence  can  in  most  cases 
be  very  easily  determined  from  an  examination  of  the 
vein. 

The  group  B5  includes  the  great  majority  of  the  minerals 
used  as  gem  stones.  Their  origin  appears  to  be  very  similar 
to  that  of  the  first  group  of  Hypogene  minerals  spoken  of. 
They  may  be  regarded  as  falling  into  two  sub-groups ; 
firstly,  those  whose  whole  constituents  existed  in  the  rock 
before  its  change ;  and  secondly,  those  whose  formation 
demanded  the  introduction  of  some  fresh  elements  from 
without  the  rock.  In  both  cases  the  molecular  rearrange- 
ment would  appear  to  have  been  brought  about  by  the  slow 
action  of  weakly  alkaline  water  under  considerable  heat  and 
pressure.  In  the  first  sub-group  a  calcareous  rock  contain- 
ing the  usual  numerous  impurities  may,  by  molecular  or 
atomic  reconstruction,  have  formed  in  it  such  minerals  as 
Idocrase,  Sphene,  Spinel  and  several  of  the  Garnets,  besides 
many  other  minerals  which  concern  us  less.  A  rock  of  a 
clayey  nature  provides  the  materials  for  the  formation  of 
lolite,  Andalusite,  some  of  the  Garnets,  and  other  compounds. 
One  point  of  great  interest  is  that  Graphite  or  other  forms 
of  carbon  diffused  in  a  rock  may  by  the  action  of  heated 
water  be  converted  into  (possibly)  a  metallic  carbide  from 


PEECIOUS  STONES.  19 

which  a  pure  form  of  carbon  may  be  deposited  in  visible 
quantity.  Anthracite  probably  thus  formed  may  be  found 
in  many  agglomerates,  and  it  was  suggested  by  J.  G.  Good- 
child  that  Diamond  may  arise  in  this  way;  certainly 
Diamonds  are  found  in  a  similar  rock  (agglomerate)  in  the 
great  mines  of  South  Africa. 

Eocks  of  eruptive  origin  have  developed  in  them  minerals 
bearing  naturally  a  relation  in  composition  to  that  of  the 
parent  rock,  so  that  one  of  basic  or  sub-basic  character  may 
have  Epidote  and  Garnets  formed  in  it. 

Of  the  second  sub-group  Tourmaline  is  a  good  example, 
though  this  mineral  usually  shows  evidence  of  dynamic 
action  as  well.  Topaz,  Beryl,  Euclase,  Phenakite  and 
Chrysoberyl  very  probably  have  some  of  their  rare  con- 
stituents brought  to  the  rock  in  this  way.  Topaz  and 
Beryl  often  occur  in  the  druses  of  plutonic  rocks  (as 
granite)  which  seem  to  have  been  formed  by  the  liberation 
of  aqueous  vapour  at  the  outer  parts  of  the  granite  mass  at 
a  later  stage  in  its  consolidation ;  these  cavities  often  have 
several  minerals  deposited  in  them  in  a  regular  succession, 
Quartz  (often  as  Cairngorm)  being  among  the  earlier,  Topaz 
and  Beryl  among  the  later.  In  such  druses,  where  the 
crystals  only  form  a  lining,  the  crystal  forms  are  idio- 
morphic,  but  where  the  crystals  have  grown  so  as  to  touch, 
they  are  allotriomorphic,  and  in  some  cases  such  growth  is 
associated  with  absorption  of  the  substance  of  the  crystal 
to  some  extent  ;  in  these  instances  the  absorption  is 
found  to  occur  almost  entirely  along  the  axis  of  greatest 
elongation. 

Tourmaline  presents  a  good  picture  of  the  changes  that 
occ  r  in  the  formation  of  itself  and  other  minerals  which 

c  2 


20  PKECIOUS   STONES. 

owe  their  origin  to  the  causes  tabulated  under  B5  and  B6. 
We  find  it  developed  as  a  secondary  mineral  in  highly- 
silicated  rocks  which  have  been  subjected  to  dynamic 
changes ;  the  beginning  of  its  formation  only  commenced 
after  many  other  changes  had  occurred  in  the  rock,  since 
its  crystals  are  attached  to  crystals  of  pre-formed  minerals, 
but  its  growth  was  completed  before  the  cessation  of  the 
movements  which  caused  the  metamorphosis ;  the  last 
movements  fractured  the  Tourmaline  crystals,  chiefly 
transversely  to  their  axis  of  greater  elongation,  and  bent 
them,  and  then  the  fissures  so  formed  were  filled  with  the 
last  of  the  rock-forming  minerals  to  consolidate,  since 
Quartz,  Felspar  and  Mica  are  found  in  these  interstices. 
The  absorption  of  the  ends  of  the  crystals  seems  to  have 
occurred  at  the  time  of  the  bending ;  it  is  comparatively 
rarely  one  finds  well  terminated  crystals,  though  specimens 
showing  the  prism  zones  well  developed  and  perfect  are 
common. 


CHAPTER  III. 

THE    PHYSICAL    PROPERTIES    OF    GEM    STONES. 

I.  THE  most  important  group  of  physical  properties  we 
have  to  deal  with  is  that  dependent  on  light.  When  light 
acts  on  a  gem  it  may — 

A.  Be  reflected  back  again. 

B.  Be  transmitted. 

0.  Produce  phosphorescence. 

A.  When  light  is  reflected  from  a  mineral  two  phenomena 
may  be  observed — 

a.  Colour. 

b.  Lustre. 

a.  White  light  falling  on  a  mineral  and  suffering  reflec- 
tion may  reveal  a  certain  colour  of  the  stone.  This  is  due 
to  certain  of  the  components  of  the  white  light  being  held 
back  or  absorbed  by  the  substance,  while  others  of  the 
coloured  rays  are  returned  to  the  eye  and  there  produce  a 
sensation  of  colour.  Should  a  stone  reflect  all  the  rays  of 
white  light  in  the  same  proportion  as  it  receives  them  it 
will  appear  white ;  if  all  or  nearly  all  the  rays  are  stopped 
it  appears  black ;  if  all  but  the  green  rays  are  stopped  we 
should  say  the  stone  was  green,  and  so  on.  It  is  very 
unsafe  to  place  much  reliance  on  colour  in  the  identification 
of  precious  stones,  as  in  many  cases  one  mineral  may  occur 
in  several  different  colours,  and  on  the  other  hand  stones  of 


22  PBECIOUS  STONES. 

very  various  kinds  have  unfortunately  become  known  by 
the  same  name  when  they  are  of  one  colour.  For  example, 
a  red  Corundum  is  Kuby,  while  a  blue  crystal  of  the  same 
mineral  is  a  Sapphire,  but  a  red  Spinel  may  also  be  sold  as 
a  Kuby ;  an  expert  eye  can  usually  distinguish  a  difference 
in  such  a  case,  but  it  is  not  absolutely  reliable. 

b.  Lustre  is  of  several  different  kinds,  usually  described 
as — 

1.  Metallic. 

2.  Adamantine. 

3.  Vitreous. 

4.  Greasy. 

5.  Eesinous. 

6.  Silky. 

7.  Pearly. 

The  lustre  may  be  of  the  varying  degrees  of  splendent, 
shining,  glistening  or  glimmering. 

By  far  the  most  important  in  the  crystallised  gem  stones 
is  the  adamantine  lustre,  and  that  we  wish  to  find  in  the 
splendent  degree — in  other  words,  the  ideal  is  to  have  the 
stones  of  as  great  a  brilliance  of  lustre  as  possible,  and 
hence  stones  which  do  not  reach  this  standard  are  thought 
less  of.  A  high  lustre  is  almost  an  essential  of  a  true  gem 
stone  at  present,  though  there  are  signs  of  a  coming  appre- 
ciation of  the  more  modest  appearance  of  some  of  the  less 
splendent  minerals. 

B.  When  the  light  is  transmitted  there  are  three 
conditions  to  be  observed  :— 

a.  Diaphaneity. 

b.  Eefraction. 

c.  Polarisation. 


PRECIOUS   STONES. 


23 


a.  Diaphaneity.      If  light  passes  through  the  mineral  so 
that  objects  can  be  seen  through  it,  the  mineral  is  said  to 
be  transparent ;  a  mineral  of  a  lesser  degree  of  diaphaneity 
is  sub-transparent.     If  light  is  transmitted,  but  in  such  a 
manner  that  we  cannot  see  through  the  substance,  the  body 
is  said  to  be  translucent ;    or  sub-translucent  if    only  a 
small  amount  of  light  passes.     If  no  light  goes  through  the 
substance  is  opaque. 

b.  Eefraction  is  of  the  highest  importance  in  the  study 
of  gem  stones ;    many 

of  the  peculiarities  of 
gems  are  due  to  this 
phenomenon. 

1.  Single  refraction. 
All  transparent 
minerals  which  are 
crystallised  in  the  cubic 
(or  isometric)  system, 
and  all  transparent 
amorphous  substances, 
are  isotropic.  If  a  ray 
of  light  A  0  (Fig.  1) 


FIG.  1. — Diagram  of  Eefraction. 


impinges  on  a  piece  of  glass  having  parallel  surfaces  F  0, 
D  G,  at  an  angle  A  0  B  with  the  normal  0  B,  it  is 
found  that  the  ray  does  not  pass  through  the  glass  in 
a  straight  line  A  O  E,  but  is  bent  or  deflected  into  the 
path  O  D,  and  on  emerging  into  the  air  again  at  D  it 
proceeds  in  a  direction  D  J  parallel  to  its  original  direc- 
tion. The  angle  A  O  B  is  called  the  angle  of  incidence, 
and  the  angle  DOC  the  angle  of  refraction.  The  lines 
B  M  and  C  N  are  proportional  to  the  sines  of  these  angles 


24  PEECIOUS  STONES. 

respectively  and  the  ratio    n  A7  is  the  index  of  refraction 

C  J\ 

when  the  incident  ray  is  passing  through  air.  All 
substances  which  transmit  light  have  a  definite  index  of 
refraction. 

All   the   components   of    white   light    are    not    equally 
refracted   by  a  given    substance,  the    rays    at   the   violet 
end  of   the  spectrum  being  most  bent  and  those   at   tre 
red  end  being  least  bent.      This  is  not  well   seen  in  the 
case  of  a  beam  of  white  light  passing  through  a  parallel- 
sided    piece     of     glass 
because    the    various 
component  rays  become 
parallel   again ;    but    if 
the  beam  pass  through 
a  prism  the  components 
are  further  separated  on 
passing  again  into  the 

FIG.  2.— Diagram  of  Dispersion.  air  (Fig.  2).  This  sepa- 
ration is  known  as  dispersion;  the  power  of  dispersion 
varies  in  different  substances,  but  is  high  in  many  of  the 
gem  stones,  particularly  in  Diamond;  to  this  property 
Diamond  owes  much  of  its  beauty,  as  the  light  being 
much  dispersed  in  the  stone  emerges  again  in  marked 
rays  of  coloured  light. 

Since  all  colours  are  not  equally  bent  in  one  given  sub- 
stance it  is  necessary  to  refer  the  index  of  refraction  to  light 
of  one  particular  colour.  The  middle  part  of  the  spectrum 
is  usually  taken  for  this  purpose ;  the  difference  in  index 
for  different  rays  is  not  great,  for  even  in  Diamond,  which 
has  such  a  great  dispersive  power,  the  index  for  the  red 


PEECIOUS  STONES.  25 

rays  is  2'407,  while  for  the  violet  rays  it  is  2'465  ;    for  the 
middle  of  the  spectrum  it  may  be  taken  as  2*44. 

Since  the  sine  of  the  angle  of  refraction  increases  with 
the  sine  of  the  angle  of  incidence,  the  former  will  have  its 
maximum  value  when  the  latter  is  unity ;  thus  if  r  be  the 
angle  of  refraction,  this  angle  will  be  at  its  greatest  when 

sin  r  =  -,  where  n  is  the  index  of  refraction ;  the  angle 

having  the  value  given  by  this  equation  is  called  the 
critical  angle.  Supposing  light  were  proceeding  from 
within  the  optically  denser  medium  and 
impinged  on  the  surface  at  this  critical 
angle,  the  ray  on  passing  into  the  rarer 
medium  would  just  skim  the  surface; 
but  if  the  angle  in  the  denser  body  were 
greater  than  the  critical  angle,  no  light 
would  pass  out  of  the  denser  medium, 
but  all  would  be  reflected  again  within 
it.  Such  a  phenomenon  is  known  as  total  FIG  3  _  Eefraction 
internal  reflection.  Applying  this  prin-  and  Internal  Ee- 
ciple  to  a  cut  gem  stone  it  is  obvious  that 
light  impinging  on  one  of  the  facets  from  air  at  any  angle  may 
be  at  least  partly  refracted  and  pass  within  the  stone,  but  that 
on  meeting  the  surface  of  a  facet  from  within  it  may  be 
wholly  turned  back.  In  Fig.  3  this  is  shown  in  the  case  of 
the  Diamond,  where  a  ray  is  shown  undergoing  first  refrac- 
tion, then  totai  Internal  reflection  three  times,  and  finally 
refraction  a  second  time.  When  the  cutting  of  precious 
stones  is  described,  it  will  be  found  that  in  the  Diamond  at 
least  there  are  definite  proportions  at  which  the  cutter 
normally  aims ;  these  proportions  ensure  the  facets  being  at 


26  PEECIOUS  STONES. 

such  an  angle  as  will  give  the  greatest  amount  of  light  back 
again  on  the  exposed  aspect  of  the  gem,  so  that  its  brilliance 
will  be  as  great  as  possible.  Another  effect  of  this  repeated 
reflection  is  to  cause  the  ray  to  pass  over  a  much  longer 
path  in  the  stone,  and  thus  the  dispersion  produced  is 
greater,  and  therefore  the  prismatic  colour  effect  is  more 
marked. 

For  the  accurate  measurement  of  refraction  an  instrument 
called  a  refractometer  is  used.  Its  action  depends  on  the 
fact  that  the  refractive  index  can  be  calculated  when  the 
angle  of  total  reflection  is  known  ;  in  the  improved  form 
devised  by  G.  F.  H.  Smith  (and  described  by  him  in  the 
"  Mineralogical  Magazine,"  vol.  xiv.  p.  83),  the  instrument 
consists  of  a  hemisphere  of  optically  dense  glass,  so 
mounted  that  its  plane  surface  makes  an  angle  of  26  degrees 
with  the  axis  of  the  instrument ;  on  the  opposite  aspect  of 
the  mount  carrying  the  hemisphere  is  a  piece  of  ground 
glass ;  arrangement  is  made  for  the  adjustment  of  this 
portion  of  the  instrument  in  relation  to  the  axis  of  the 
tube ;  a  correcting  convex  lens  is  placed  close  to  the  hemi- 
sphere and  in  the  tube ;  at  the  other  end  of  the  tube  is  a 
positive  eye-piece  capable  of  sliding  adjustment,  and  pro- 
vided with  a  totally  reflecting  glass  prism  to  allow  of  the 
instrument  being  held  in  a  convenient  position.  A  scale  is 
provided  by  means  of  which  the  index  can  be  read  to  two 
places  of  decimals  at  least.  In  using  the  instrument  the 
gem  to  be  observed  is  placed  on  the  plane  surface  of  the 
hemisphere  and  moistened  with  a  drop  of  a  liquid  of  higher 
refractive  index  than  itself;  on  looking  through  the  eye- 
piece a  shadow  is  seen  crossing  the  scale  in  the  form  of  a 
circular  arc.  By  using  a  hemicylindrical  glass  and  a 


PEECIOUS  STONES.  27 

cylindrical  lens  the  line  of  separation  between  light  and 
dark  appears  as  a  straight  line.  The  range  is  from  1*40  to 
1*76  in  value  of  n. 

2.  Double  refraction.  All  crystals  except  those  belong- 
ing to  the  cubic  system  show  double  refraction  ;  that  is  to 
say,  a  ray  of  monochromatic  light  passing  through  such  a 
crystal  is  not  only  deviated  from  its  direction  without  the 
crystal,  but  is  turned  in  two  directions,  part  of  it  going  in 
one  path  and  part  in  another ;  the  angle  between  these  two 
paths  is  very  small,  never  more  than  a  few  degrees  at  most, 
and  in  some  cases  is  so  small  that  the  two  rays  would  seem 
to  be  one  except  when  determined  by  special  apparatus. 

This  double  refraction  can  be  readily  shown  if  we  take  a 
piece  of  Calcite  of  the  clear  variety  known  as  Iceland  Spar 
or  Doubly  Kefracting  Spar,  of  the  form  it  naturally  assumes 
when  broken,  and  view  through  it  a  mark,  such  as  a  cross, 
on  a  piece  of  paper.  Two  crosses  appear,  both  somewhat 
removed  from  the  position  we  see  the  original  mark  in, 
when  nothing  is  interposed,  but  one  more  displaced  than 
the  other.  On  rotating  the  Iceland  Spar,  one  cross  appears 
to  move  round  the  other.  Similarly,  if  we  view  an  object 
through  a  cut  specimen  of  one  of  the  doubly  refracting  gems 
such  as  Peridot,  we  shall  see  two  images  of  the  object 
through  each  of  the  facets  on  the  part  of  the  gem  away 
from  the  eye.  On  rotating  a  piece  of  Iceland  Spar  as 
above,  we  should  also  notice  that  in  certain  positions  the 
two  images  were  further  apart  than  in  others ;  now  if  the 
mineral  were  cut  in  a  particular  direction  and  the  surfaces 
polished,  on  looking  at  the  cross  through  iis  we  should  only 
see  one  image ;  in  other  words,  it  is  singly  refracting  in 
that  direction.  Such  directions  are  known  as  optic  axes ; 


28  PEECIOUS  STONES. 

all  minerals  crystallising  in  the  hexagonal  and  tetragonal 
systems  have  one  such  axis,  and  it  coincides  with  the 
principal  axis  of  the  crystal.  Minerals  of  the  remaining 
crystallographic  systems  (that  is,  the  orthorhombic,  the 
monosymmetric  or  monoclinic,  and  the  triclinic)  have  two 
such  axes ;  all  crystals  with  double  refraction  are  anisotropic. 

The  property  of  double  refraction  can  be  made  use  of  in 
the  identification  of  certain  gem  stones.  If  on  looking 
through  a  cut  gem  we  see  two  images  of  an  object 
through  one  pair  of  facets,  we  know  that  the  gem  is  a 
doubly-refracting  one  ;  but  if  we  cannot  be  sure  of  seeing 
two,  we  cannot  say  at  once  that  it  is  singly  refracting,  as 
there  are  some  possible  fallacies ;  firstly,  we  may  be  looking 
along  the  optical  axis  of  a  uniaxial  crystal,  or  along  one  of 
the  axes  of  a  biaxial  crystal,  in  either  of  which  cases  only  one 
image  would  appear;  secondly,  the  separation  of  the  two 
images  may  be  too  slight  to  be  observed  by  the  unaided  eye. 

c.  Now,  if  a  ra,y  of  white  light  be  reflected  from  the 
surface  of  glass  at  a  certain  angle,  a  particular  set  of  the 
light  undulations  are  suppressed  and  the  remaining  undula- 
tions can  no  longer  be  reflected  in  all  directions;  if 
these  residual  vibrations  be  received  on  another  plate  of 
glass  inclined  to  the  rays  at  the  same  angle,  but  with  the 
plane  of  incidence  at  right  angles  to  the  plane  of  incidence 
on  the  first  piece  of  glass,  no  light  is  reflected  from  the 
second  glass.  If  now  between  the  two  pieces  of  glass  a 
crystal  belonging  to  the  cubic  system,  or  an  amorphous 
transparent  body,  be  placed,  there  is  still  no  light  reflected 
to  the  eye.  Should,  however,  an  anisotropic  body  be 
interposed,  light  will  be  transmitted  to  the  eye  again, 
unless  perchance  the  optic  axis  coincides  with  the  direction 


PBEOIOUS  STONES.  29 

of  the  ray  of  light  between  the  two  sheets  of  glass.  Such 
an  instrument  is  a  simple  form  of  the  polariscope.  More 
frequently  two  prisms  of  Iceland  Spar  cut  and  mounted  in 
a  particular  way  are  used  to  polarise  and  analyse  the 
light;  such  prisms  are  called  "Nicol's  prisms  "  ;  the  prisms 
are  mounted  so  as  to  be  capable  of  complete  rotation  with 
regard  to  one  another,  and  there  are  two  positions  in  the 
complete  revolution  of  maximum  extinction  of  light ;  when 
the  prisms  are  in  one  of  these  two  positions,  they  are  said 
to  be  "  crossed."  Now  a  singly-refracting  body  placed 
between  crossed  Nicol's  prisms  allows  no  light  to  pass 
whatever  the  position  of  the  body,  but  in  the  examination 
of  a  gem  we  must  use  two  or  even  three  positions  to  make 
sure  we  are  not  dealing  with  a  doubly  refracting  substance 
placed  with  the  optic  axis  in  the  axis  of  the  instrument.  In 
examining  a  gem  it  must  be  first  placed  resting  in  the 
carrier  on  its  small  back  facet,  so  as  to  give  the  light  every 
opportunity  of  being  transmitted  through  the  stone.  If 
there  is  a  possibility  that  total  internal  reflection  is 
preventing  the  light  reaching  the  eye,  we  may  overcome 
the  possible  fallacy  by  immersing  the  gem  in  a  liquid  of 
similar  refractive  index ;  for  this  purpose  methylene  iodide 
or  mono-bromo-naphthalene  may  be  used.  When  a  doubly- 
refracting  stone  is  placed  in  the  right  position,  we  shall  find 
on  rotating  it  that  there  are  four  positions  in  the  360°  in 
which  there  is  maximum  lightness,  due  to  the  light  being  so 
altered  in  its  passage  through  the  gem  that  it  can  pass 
through  the  analyser. 

One  other  possible  fallacy  remains  to  be  mentioned. 
Some  singly-refracting  substances  show  what  is  known  as 
anomalous  double  refraction  ;  this  IB  due  to  strains  set  up 


30  PBECIOUS  STONES. 

in  the  substance.  They  can  be  distinguished  under  the 
polariscope  by  the  feeble  change  from  light  to  dark  as  they 
are  rotated  and  by  the  light  not  being  uniform  over  the 
whole  field  of  view. 

Another  important  phenomenon  arising  from  double 
refraction  remains  to  be  considered.  In  an  anisotropic 
substance  the  vibrations  composing  the  one  ray  are  at 
right  angles  to  those  composing  the  other  ray.  Now,  a 
different  absorption  of  light  occurs  in  these  two  planes,  and 
as  a  consequence  images  of  different  colours  are  seen; 
this  is  known  as  pleochroism.  For  the  observation  of 
these  colours  an  instrument  known  as  a  dichroscope  is 
used  ;  it  consists  of  a  cleaved  piece  of  Iceland  Spar  mounted 
in  a  tube  having  a  lens  at  one  end  and  a  square  aperture 
at  the  other.  The  lens  can  be  adjusted  to  give  focussed 
images  of  the  aperture,  and  at  the  end  where  the  aperture 
is  a  carrier  to  hold  the  gem  is  fitted  so  that  it  can  be 
rotated  around  the  axis  of  the  tube.  A  singly-refracting 
gem  placed  over  the  square  aperture  gives  two  images  of 
exactly  the  same  colour ;  but  a  coloured  doubly-refracting 
stone  gives  two  images  of  distinctly  different  colours.  Care 
must  be  taken  to  move  the  gem  so  as  to  ensure  viewing  in 
other  than  an  optic  axis. 

C.  Phosphorescence  is  seen  in  some  minerals  after 
exposure  to  light.  For  example,  a  Diamond  that  has  been 
exposed  to  sunlight  and  then  taken  into  a  dark  room  gives 
off  a  soft  light.  The  phenomenon  is  not  only  produced  by 
the  action  of  light,  for  some  minerals  show  it  on  being 
rubbed  (e.g.,  Diamond  and  Agate),  while  others  show  it  on 
being  heated  (e.g.,  Topaz).  Fluor  Spar,  Aragonite,  and 
Kunzite  also  phosphoresce  strongly. 


PRECIOUS  STONES.  31 

Some  other  phenomena  in  relation  to  light  remain  to  be 
noticed.  Some  minerals,  especially  Labradorite,  when 
viewed  in  certain  directions  are  seen  to  give  a  brilliant 
colour  effect.  This  is  in  no  way  due  to  any  material  pig- 
ment, but  wholly  to  the  minute  structure  of  the  stone 
causing  an  optical  colour  effect,  as  is  caused  in  the  feathers 
of  many  birds  by  their  structure.  This  effect  is  known  as 
change  of  colour.  Iridescence  is  caused  in  a  somewhat 
similar  way  by  interference  of  light  in  minute  air-filled 
cracks  in  the  mineral.  It  is  often  seen  from  natural  flaws 
in  Quartz  crystals,  and  is  sometimes  intentionally  produced 
by  suddenly  cooling  a  heated  piece  of  this  mineral.  The 
colour  of  Opal  is  sometimes  ascribed  to  this  cause,  and 
sometimes  referred  to  the  bending  and  dispersion  of  the 
light  rays.  Minute  crystalline  structure  may  also  produce 
the  quiet  soft  change  of  light  seen  in  the  Adularia  or  Moon- 
stone so  well.  The  same  effect  occurs  even  more  markedly 
in  some  specimens  of  Chrysoberyl,  causing  a  streak  of 
light  to  appear  on  turning  the  stone,  which  is  then, 
from  its  appearance,  called  Cat's  Eye.  Other  minerals 
showing  this  change  are  known  under  the  same  name ;  for 
example,  some  specimens  of  Quartz,  though  in  this  case  it 
is  due  rather  to  a  fibrous  structure  than  to  a  minute  plate- 
like  arrangement.  The  appearance  in  this  case  is  called 
chatoyancy. 

Asterism,  so  often  seen  in  crystals  of  Sapphire  cut  at 
right  angles  to  the  vertical  axis  of  the  crystal,  is  due  either 
to  minute  canals  crossing  in  one  plane  at  angles  of  120°,  or 
to  an  optical  effect  from  twin-plates  in  the  crystal.  Fluor- 
escence is  a  change  of  colour  in  a  mineral,  as  seen  when 
viewed  first  by  reflected  and  then  by  transmitted  light. 


32  PEECIOUS  STONES. 

Fluor  Spar  (from  which  name  the  term  is  derived)  shows  it 
well,  as  does  also  Amber. 

Absorption  bands  in  the  spectrum  are  only  seen  in  two 
minerals ;  in  both  cases  their  discovery  was  due  to  Pro- 
fessor Church.  Zircon  shows  some  black  bands  when 
examined  in  the  spectrum  of  white  light,  due  to  the  presence 
of  traces  of  uranium.  Almandine  also  shows  some  black 
bands,  in  this  case  in  the  green  portion  of  the  spectrum. 

The  effect  of  Rontgen  rays  on  gems  is  now  of  much 
importance,  especially  in  the  case  of  the  Diamond,  for  this 
is  very  transparent  to  these  rays,  while  many  of  its  would-be 
imitators,  as  glass,  Quartz,  white  Topaz,  etc.,  are  opaque,  and 
these  cast  shadows.  So  also  the  red  and  blue  shades  of 
Corundum  (Ruby  and  Sapphire)  are  partly  transparent,  while 
their  imitators,  Balas  Ruby  (Spinel  of  rose  red  colour)  and 
blue  Tourmaline,  are  opaque.  Exposure  to  Rontgen  rays 
or  to  the  emanations  of  radium  may  cause  some  minerals 
to  phosphoresce  (e.g.  Kunzite) ;  and  Crookes  has  shown  that 
some  minerals  phosphoresce  strongly  when  exposed  in  a 
high  tension  electric  current  in  a  very  rarefied  atmosphere. 
Thus  Ruby  shows  a  strong  red  light,  Sapphire  a  blue,  and 
Diamond  a  bright  green  light. 

Subjoined  is  a  table  of  the  refractive  index  of  the 
principal  gems : — 

Diamond  .  .           2-44  Orthoclase  .  .  1-53— 1 -52 

Fluor  Spar  .  .           1-44  Diopside  .  .  .  1-70— 1'67 

Quartz     .  .  .  1-55— 1-54  Beryl       .  .  .  1-58— 1 -57 

Opal         ...           1-48  Cordierite  .  .  1-55— 1-56 

Corundum  .  .  1-77— 1-76  Pyrope     .  .  .  1-79 

Spinel      .  .  .           1'72  Almandine  .  .  1'77 

Chrysoberyl  .  .  1 '76— 1-75  Hessonite  .  .  1'74 

,  .  .  1-66— 1-49  QHvine     ,  .  1-70—  l-6(j 


PEECIOUS   STONES. 


33 


Phenakite 
Dioptase 
Idocrase 
Zircon . 
Topaz  . 
Andalusite 
Cyanite 
Euclase 


1-67—  1-65 
1-72—  1-67 

Epidote 
Axinite 

.     1-76—1-73 
.     1-68—1-67 

1-72—  1-71 

Tourmaline  . 

.     1-64—1-62 

1-97—  1-92 
1-63—1-62 
1-64—1-63 
T72  (mean) 

Sphene 
Apatite 
Gypsum 
Amber  . 

1"90  (mean) 
1*66  (maximum) 
.     1-53  (mean) 
1-5 

1-67—1-65 

II.  PHYSICAL  PROPERTIES  DEPENDENT  ON  HEAT. 

The  forms  of  radiant  energy,  heat  and  light,  are  so 
closely  related  that  we  might  expect  their  manifestations  in 
relation  to  the  precious  stones  to  be  much  alike.  This  is 
so,  for  heat  rays  may  be  reflected,  refracted,  or  absorbed,  as 
may  light  rays.  Effects  akin  to  polarisation  may  be 
observed  too,  but  none  of  these  effects  are  of  the  same 
importance  in  the  general  consideration  of  gem  stones  as 
are  the  results  of  the  action  of  light.  A  few  facts  may, 
however,  be  briefly  stated  as  of  general  interest. 

Heat  easily  passes  through  Fluor  Spar,  hence  it  is  said  to 
be  diathermanous,  while  Tourmaline,  Gypsum  and  Amber 
are  almost  opaque  to  heat  rays. 

The  conductivity  of  heat  is  found  to  vary  in  different 
minerals  and  in  different  directions  in  relation  to  the 
crystal  axes  ;  the  coefficient  of  expansion  is  different  in 
these  several  directions  in  many  cases,  and  this  brings 
about  changes  in  the  optical  characters  under  these  con- 
ditions. On  the  whole  the  precious  stones  are  good 
conductors  of  heat  as  niine'ral  substances  go,  and  hence  it 
is  stated  in  Mr.  H.  Spencer's  translation  of  Max  Bauer's 
"  Precious  Stones,"  that  this  may  sometimes  be  used  as  a 
means  of  distinguishing  between  a  true  and  a  false  gem ; 

p.s.  D 


34  PRECIOUS  STONES. 

when  a  precious  stone  is  breathed  on  its  good  conductivity 
causes  the  breath  to  condense  on  its  surface  quickly  and  to 
quickly  evaporate  again,  whereas  on  a  glass  imitation  both 
actions  occur  more  slowly. 

Fusibility.  Most  gem  stones  fuse  with  difficulty,  if  at 
all,  before  the  blowpipe  ;  red  Garnet,  however,  is  moderately 
fusible,  and  where  thin  splinters  of  the  rough  stones 
can  be  obtained  this  property  may  be  made  use  of  in 
identification. 

III.  ELECTRICAL  AND  MAGNETIC  PROPERTIES. 

A  surface  charge  of  high  potential  electricity  can  be 
imparted  to  some  precious  stones  in  a  much  greater  degree 
than  others.  When  produced  by  rubbing  with  a  dry  cloth 
the  charge  is  positive  in  cut  gems,  except  in  the  case  of 
Amber,  which  becomes  negatively  electrified.  The  presence 
of  such  a  charge  can  be  demonstrated  by  the  electroscope 
or  other  similar  instrument.  Most  minerals  soon  lose  their 
charge,  even  in  dry  air,  but  Topaz,  Sapphire  and  Diamond 
retain  their  charge  for  longer  periods,  chiefly  in  the  case 
of  Topaz  and  least  with  the  Diamond.  Electricity  developed 
in  uncut  gems  other  than  the  Diamond  is  negative;  Calcite, 
Topaz,  Fluor  Spar  and  Quartz  show  electric  phenomena  on 
pressure,  especially  Calcite. 

When  some  precious  stones  are  heated,  electricity  is 
developed  on  them  ;  this  is  known  as  pyroelectricity. 
Axinite,  Tourmaline  and  Topaz  show  it  well ;  a  crystal  of 
Tourmaline  on  heating  to  about  150°  C.  becomes  positively 
electrified  at  one  termination  and  negatively  at  the  other ; 
if  now  it  be  suspended  by  a  non-conducting  thread  it  will 


PKECIOUS   STONES.  35 

act  as  a  magnet ;  on  cooling,  the  charges  on  the  poles 
reverse,  positive  becoming  negative.  If  a  crystal  with  such 
a  charge  be  dusted  with  a  fine  mixture  of  sulphur  and  red 
lead,  the  yellow  sulphur  will  be  attracted  to  the  portions 
charged  with  positive  electricity,  while  the  red  lead  goes  to 
the  negatively  charged  portions. 

The  pyroelectric  behaviour  of  Tourmaline  and  Topaz  may 
be  made  use  of  to  distinguish  these  minerals  from  others  of 
similar  colour. 

Though  some  minerals  show  magnetic  properties,  only 
one  is  of  any  importance  in  the  present  case  :  this  is  Iserine, 
one  of  the  titaniferous  iron  ores,  which  has  been  used  as  an 
ornamental  stone. 

IV.  SPECIFIC  GRAVITY. 

The  specific  gravity  of  a  substance  is  the  ratio  of  the 
weight  of  a  given  volume  of  that  substance  to  the  weight  of 
an  equal  volume  of  a  standard  substance.  Water  is  always 
taken  as  the  standard  in  dealing  with  minerals.  Specific 
gravity  is  of  the  greatest  importance  in  dealing  with  pre- 
cious stones,  as  it  affords  a  means  of  identifying  many  of 
them  when  cut  and  polished,  without  in  any  way  damaging 
the  stone. 

There  are  many  methods  of  determining  the  specific 
gravity  of  a  substance ;  three  will  be  briefly  described  here 
applicable  to  the  cases  (a)  where  there  are  many  small  frag- 
ments of  the  mineral  available ;  (b)  where  it  is  desired  to 
deal  with  a  small  cut  stone,  and  (c)  where  a  relatively  large 
specimen  can  be  used.  Of  course  the  use  of  the  various 
methods  is  not  thus  restricted ;  they  are  merely  cited  as 
examples. 

D  2 


36  PBECIOU3  STONES. 

(a)  Method  by  Specific  Gravity  Bottle. 

When  a  solid  is  entirely  immersed  in  water  it  is  obvious 
that  it  displaces  a  volume  of  water  equal  to  its  own  volume. 
Thus  if  W  =  weight  of  the  substance  in  air 
and  w  =  weight  of  the  water  displaced, 

then  Sp.  gr.  =  — . 
w 

A  small  flask  of  very  thin  glass,  provided  with  an  accurately- 
fitting  glass  stopper  (through  which  a  small  hole  is  drilled), 
is  filled  with  water ;  the  stopper  is  then  inserted  so  as  to 
force  a  little  water  out  through  the  narrow  aperture  in  the 
stopper  ;  the  bottle  is  carefully  dried  outside.  The  sub- 
stance to  be  examined,  preferably  in  small  fragments,  is 
accurately  weighed  and  the  weight  noted  ;  let  the  weight 
be  W.  Now  weigh  the  bottle,  full  of  water,  and  the  sub- 
stance together  in  the  balance,  and  let  the  combined  weight 
be  x.  Now  remove  the  stopper  and  carefully  place  the 
mineral  in  the  bottle,  taking  care  that  the  fragments  do 
not  carry  air-bubbles  with  them ;  replace  the  stopper  and 
again  dry  and  weigh  the  bottle ;  let  this  weight  be  y. 
Now  x  —  y  is  equal  to  the  weight  of  the  water  displaced,  or, 
in  other  words,  to  the  weight  of  a  volume  of  water  equal  to 

V7 

the  volume  of  the  mineral.     Hence  -        -  is  equal  to  the 

x  —  y 

specific  gravity  of  the  substance.  In  all  accurate  deter- 
minations a  temperature  of  4°  C.  should  be  maintained  to 
ensure  the  water  remaining  at  the  maximum  density. 

(b)  Method  by  Dense  Solutions. 

A  small  number  of  liquids  may  be  obtained  which  have 
a  densit}^  equal  to  or  greater  than  most  of  the  precious 


PEECIOUS   STONES.  37 

stones.  Sonstedt's  solution  is  a  saturated  watery  solution 
of  the  double  iodide  of  mercury  and  potassium  of  sp.  gr.  2'77 ; 
it  mixes  with  water  without  any  marked  change  in  the 
volume,  and  hence  may  have  its  specific  gravity  lowered  in 
proportion  to  the  quantity  of  water  added.  The  boro- 
tungstate  of  cadmium  has  also  been  used.  More  recently, 
however,  methylene  iodide  has  been  used  ;  this  is  a  carbon 
compound  of  the  formula  CH^I^  and  has  a  density  of 
nearly  3'33  at  15°  C. ;  owing  to  its  high  coefficient  of 
expansion  it  is  important  to  use  it  at  a  definite  known 
temperature ;  it  has  the  advantages  of  mixing  freely  with 
benzine  (sp.  gr.  '88);  of  being  light-coloured,  so  that  the 
mineral  under  test  can  be  easily  seen ;  and  mobile,  so  that 
the  test  specimen  can  move  freely.  By  means  of  benzine 
or  methylene  iodide  or  a  mixture  of  the  two,  any  density 
between  '88  and  3'33  can  be  obtained.  Further,  by  satur- 
ating methylene  iodide  with  iodine  and  iodoform  its  density 
can  be  raised  as  high  as  3*6.  The  principal  gem  stones 
with  a  higher  specific  gravity  than  3'6  are  Corundum,  Spinel, 
Chrysoberyl,  the  Garnets,  Zircon  and  Cyanite.  The  most 
convenient  way  of  using  these  solutions  is  to  have  them  in 
four  wide-mouthed  stoppered  bottles  of  glass.  No.  1  con- 
tains the  saturated  solution  of  iodine  and  iodoform  in 
methylene  iodide,  and  has  a  sp.  gr.  of  3'6 ;  No.  2  contains 
pure  methylene  iodide,  sp.  gr.  3*3 ;  No.  3  a  dilution  of 
methylene  iodide  with  benzine  to  sp.  gr.  3'0  ;  and  No.  4  a 
similar,  but  further,  dilution  to  sp.  gr.  2*65.  The  specific 
gravity  of  these  solutions  must  be  tested  from  time  to  time 
by  some  such  convenient  means  as  the  use  of  specific 
gravity  beads,  which  are  hollow  glass  beads  so  weighted 
that  they  neither  float  nor  sink  in  a  liquid  of  a  certain 


38  PRECIOUS   STONES. 

density,  the  numerical  equivalent  of  which  is  marked  on 
the  bead.     Thus,  when  a  mineral  is  placed  in,  say,  No.  1 
bottle,  and  is  found  to  sink,  we  know  it  is  of  a  density 
greater  than  3*6.     A  mineral  of  a  sp.  gr.  of  2'8  would  float 
in  solution  No.  3,  but  would  sink  in  solution  No.  4.     Thus 
we  may  divide  all  the  specimens  tested  into  five  groups, 
and  thus  greatly  aid  their  identification.     If  it  is  desired  to 
accurately  determine  the  specific  gravity  of  a  specimen  we 
may  select  a  solution  in  which  it  floats,  and  then  dilute 
with  benzine  till  it  neither  floats  nor  sinks.     It  is  then  of 
the  same  density  as  the  solution,  and  this  is  determined  by 
the  specific  gravity  bottle  described  in  method  (a),   then 
weighing   the   same  bottle  full   of   water  at  4°  C.,   again 
emptying  and  drying  the  bottle,  and  finally  weighing  it 
full  of  the  solution  in  question.     Then  (weight  of  bottle 
with  solution  less  weight  of  bottle)  divided  by  (weight  of 
bottle  with   water  less  weight  of  bottle),  is  equal  to  the 
specific  gravity  of  the  solution,  and  therefore  of  the  gem  to 
be  determined.     In  removing   a  gem  from  one  bottle  of 
solution  to  another  care  must  be  taken  to  dry  it,  or  else  the 
solutions  will  become  mixed  and  altered  in  density.     The 
bottles  containing  the  four  solutions  must  be  kept  in  the 
dark   also,  to   prevent  decomposition    with   separation    of 
iodine,  which  would  not  only  cause  a  dark  colour  to  appear, 
but  would  also  alter  the  density.     Such  solutions  may  also 
be    used    to    separate   particles   of   various   minerals   for 
analysis. 

Still  more  recently  thallium-silver  nitrate,  Ag  Tl  (N0s)z, 
a  solid  salt,  has  been  used ;  with  the  addition  of  a  little 
water  it  remains  fluid  at  as  low  a  temperature  as  50°  C. 
The  pure  salt  melts  at  75°  C.,  and  forms  a  transparent 


PRECIOUS  STONES.  39 

liquid  of  specific  gravity  of  4'8  ;  a  very  small  quantity  of 
water  considerably  lowers  the  density  of  the  resulting 
liquid  ;  in  using  this  method  care  must  be  taken  to  allow 
for  temperature — in  other  words,  the  density  of  the  solu- 
tion must  be  determined  at  the  same  temperature  as  the 
solution  was  at  when  the  stone  was  being  tested  in  it. 

(c)  Method  with  the  Hydrostatic  Balance. 

In  this  method  any  delicate  balance  may  be  used,  but 
there  are  many  special  forms  made  for  the  purpose  which 
are  very  convenient  in  use.  The  method  is  more  adapted 
to  the  examination  of  larger  specimens.  If  the  scale  pans 
come  close  down  to  the  platform  of  the  balance  one  pan 
must  be  removed  and  a  long  fine  hair  or  strand  of  silk 
attached  in  its  place ;  the  remaining  pan  is  now  exactly 
counterpoised  by  attaching  a  suitable  weight  at  the  end  of 
the  beam  where  the  detached  pan  was.  A  small  beaker 
partly  full  of  water  is  arranged  so  that  a  gem  attached  to 
the  end  of  the  hair  will  be  under  the  surface  of  the  water 
when  the  instrument  is  in  a  balanced  position  ;  this  beaker 
can  then  be  removed  from  its  support  and  the  gem  attached 
to  the  end  of  the  silk  or  hair  by  slinging  it  in  a  small  neat 
loop.  The  exact  weight  of  the  gem  in  air  is  then  ascer- 
tained ;  the  beaker  is  now  replaced,  allowing  the  stone  to 
be  completely  immersed  in  water  but  having  as  little  of  the 
hair  as  possible  in  water.  The  weight  in  water  is  now 
determined.  The  difference  between  the  weight  in  air  and 
the  weight  in  water  is  the  weight  of  a  volume  of  water 
equal  to  the  volume  of  the  stone,  therefore  the  weight  of 
the  stone  in  air  divided  by  this  difference  is  the  specific 
gravity  of  the  stone. 


40 


PRECIOUS   STONES. 


A  very  full  and  exact  account  of  these  and  other  methods 
of  determining  specific  gravity  will  be  found  in  Max  Bauer's 
work  above  mentioned.  In  the  following  list  of  the  specific 
gravities  of  precious  stones  the  minerals  are  arranged  on 
the  basis  of  composition  that  will  be  followed  in  the  systematic 
description. 


Diamond 

3-50—3-52 

Garnet  :  Topazolite  . 

3-65—3-85 

Fluor  Spar 

3-02—3-20 

Demantoid 

3-83 

Quartz     .         . 

2-5-2-8 

Uvarovite  . 

3-42 

Opal 

2-19—2-20 

Olivine    . 

3-33—3-44 

Corundum 

3-93—4-08 

Phenakite 

2-95 

Spinel 

3-60-3-63 

Dioptase  . 

3-27—3-35 

Chrysoberyl     . 

3-68—3-75 

Idocrase  . 

3-35—3-45 

Calcite     . 

2-69—2-75 

Zircon 

4-6—4-7 

Malachite 

3-71—  4-01 

Topaz 

3-4—3-6 

Orthoclose 

2-53—2-59 

Andalusite 

3-10—3-19 

Microcline 

2-44 

Cyanite    . 

3-58—3-68 

Albite      . 

2-54—2-64 

Euclase   . 

3-05 

Oligoclase 

2-63—2-74 

Epidote    . 

3-35—3-5 

Labradorite 

2-67—2-76 

Axinite    . 

3-29—3-30 

Pyroxene 

3-2—3-4 

Prehnite  . 

2-92—3-01 

Spodumene 

3-15—3-20 

Tourmaline 

3-02—3-10 

Jadeite     . 

3-3 

Staurolite 

3-73—3-74 

Amphibole 

3-0 

Serpentine 

2-47—2-60 

Crocidolite 

3-2—3-3 

Sphene    . 

3-35—3-45 

Beryl       . 

2-67—2-75 

Apatite    . 

3-16—3-22 

Cordierite 

2-60—2-72 

Turquois  . 

2-62—3-0 

Lapis  Lazuli    . 

2-38—2-45 

Gypsum  . 

2-28—2-33 

Garnet  :  Gross  ular  . 

3-44—3-62 

Amber     . 

1-08 

Pyrope 

3-70—3-78 

Jet  . 

1-02 

Almandine 

3-95—4-29 

V.  PROPERTIES  DEPENDENT  ON  THE  STATE  OF  AGGREGATION. 

Of  the  many  properties  of  minerals  in  general,  falling 
under  this  head,  only  two  specially  concern  us  in  the  study 
of  precious  stones — fracture  and  brittleness.  Fracture  can 


OF  THE 

UNIVERSITY 

OF 


5IOUS  STONES.  41 


be  seen  in  most  rough  precious  stones ;  it  must  be  dis- 
tinguished from  cleavage  (q.v.)  ;  fractured  surfaces,  though 
they  approach  geometrical  planes  in  some  cases,  are  never 
true  planes.  When  the  fracture  is  flat  or  nearly  flat  it  is 
said  to  be  "  even  "  ;  this  is  seen  in  some  Jaspers.  Should 
it  be  rougher  and  covered  with  minute  points  it  is  "  uneven," 
as  in  Lapis  Lazuli;  when  still  more  rough  it  is  "hackly." 
When  the  broken  surface  shows  the  smooth  curves  so  well 
seen  in  a  broken  piece  of  thick  glass,  the  fracture  is 
"conchoidal  "  (i.e.  shell-like),  this  is  well  seen  in  Quartz 
and  many  of  the  gem  stones.  Where  a  gem  stone  has 
been  damaged,  as  by  a  blow,  but  without  separation  of  the 
fragments,  a  crack  may  often  be  seen  reflecting  beautiful 
prismatic  colours  (c.f.  refraction).  This  is  occasionally 
made  use  of  in  stones  that  have  no  intrinsic  beauty 
of  colour  as  in  Quartz ;  but  in  a  highly  refracting 
gem  any  flaw  of  the  sort,  especially  if  situated  at 
the  back  part  of  the  cut  stone,  greatly  detracts  from  the 
brilliance,  so  that  when  a  flaw  develops  before  the  stone  is 
cut,  the  size  of  the  finished  stone  and  the  direction  of  the 
cuts  are  arranged  to  eradicate  such  blemishes.  This  was 
exemplified  in  the  case  of  the  Koh-i-noor,  which  as 
exhibited  at  the  Crystal  Palace  weighed  186 -^  carats,  but 
which  was  afterwards  re-cut  by  Messrs.  Garrard,  when  it 
weighed  102J  carats. 

Brittleness  depends  very  largely  on  the  grosser  structure 
of  the  stone  ;  where  this  is  minutely  fibrous,  as  in  Crocidolite 
or  Malachite,  there  may  be  considerable  tenacity,  though 
the  hardness  of  these  two  minerals  is  very  different ;  at  the 
same  time  the  brittleness  depends  partly  on  the  hardness, 
and  also  on  the  presence  or  absence  of  a  cleavage. 


42  PEECIOUS  STONES. 

VI.  HARDNESS. 

All  the  true  gems  are  essentially  hard.  A  mineral  does  not 
fulfil  the  commonly  accepted  idea  of  a  gem  unless  it  is  hard  ; 
but  the  degree  of  hardness  varies  considerably.  An  arbitrary 
scale  devised  by  Mohs  is  used  to  express  the  relative  hard- 
ness of  different  minerals.  Ten  different  minerals  of 
dissimilar  hardness  are  chosen  ;  these  are  (No.  1  being  the 
softest)  — 

1.  Talc. 

2.  Gypsum. 

3.  Calcite. 

4.  Fluor  Spar. 

5.  Apatite. 

6.  Orthoclase  Felspar. 

7.  Quartz. 

8.  Topaz. 

9.  Sapphire. 
10.  Diamond. 

If  we  were  dealing  with  an  uncut  gem  on  which  a  scratch 
would  not  be  of  great  importance  we  might  first  apply  a  sharp 
corner  of  it  to  the  test  stones,  beginning  with  the  softest 
until  we  come  to  one  it  will  not  scratch  ;  if  on  reversing  the 
positions  the  test  stone  does  not  scratch  the  stone  under 
examination,  we  know  that  the  two  are  of  equal  hardness  ; 
should  it  scratch  the  examined  stone  we  know  the  latter 
has  a  hardness  between  the  test  stone  that  will  scratch  it 
and  the  test  stone  next  in  the  series  below.  By  approxi- 
mation we  may  fix  the  hardness  at,  say,  7'25  or  7*5  when  the 
examined  stone  just  scratches  Quartz  and  is  easily  scratched 
by  Topaz.  In  the  case  of  cut  gems  we  usually  have  to  be 


PEECIOUS  STONES.  43 

content  with  finding  what  is  the  highest  member  of  the 
series  of  test  stones  it  will  scratch  ;  in  some  cases  we  may  be 
able  to  try  to  scratch  the  cut  gem  on  the  girdle  or  part  by 
which  its  mount  clasps  it.  Many  minerals  show  a  different 
degree  of  hardness  on  different  crystal  faces  or  in  different 
directions  ;  thus  Cyanite  shows  a  variation  of  hardness  in 
different  directions  between  5  and  7  on  Mohs'  scale.  We 
must  be  careful  to  distinguish  between  a  scratch  on  a  test  stone 
and  a  streak  of  broken-down  fragments  of  the  tested  'speci- 
men ;  if  it  be  a  true  scratch  the  mark  will  of  course  remain 
on  brushing  with  a  soft  camel-hair  brush.  It  is  necessary 
to  examine  the  mark  with  a  lens  incases  of  doubt.  In  test- 
ing, no  more  force  should  be  used  than  is  just  sufficient  to 
produce  the  scratch,  and  no  more  scratch  should  be  made 
than  is  necessary.  Where  the  test  stones  are  of  a  cleavable 
mineral,  clean  cleavage  planes  (c.f.  Cleavage)  will  be  found 
the  most  suitable  for  trying  the  hardness  on.  A  steel  point 
is  as  good  an  instrument  as  one  can  have  for  a  single  test ; 
good  carbon  steel  tempered  to  a  pale  straw  colour  will  just 
scratch  quartz  under  favourable  conditions ;  more  often  the 
steel  can  be  scratched  by  quartz.  Thus  a  steel  point  may 
be  taken  as  of  No.  7  hardness ;  what  is  called  "  gem- 
hardness,"  that  of  the  true  gem  stones,  is  greater  than  7. 
It  should  be  noted  that  the  newer  "  high  speed  "  steel  is  a 
great  deal  harder  than  ordinary  carbon  steel.  As  glass  is 
easily  scratched  by  steel,  such  a  steel  point  will  readily 
serve  to  distinguish  glass  imitations  of  precious  stones  in 
most  cases. 

A  tabular  statement  of  the  hardness  of  precious  stones  is 
given  below.  It  should  be  noted  that  under  certain 
species  are  included  in  some  cases  several  varieties,  and 


44 


PRECIOUS   STONES. 


this  accounts  for  much  of  the  variation.  For  example, 
Quartz  in  its  crystalline  forms  of  Eock  Crystal,  Amethyst, 
etc.,  has  the  standard  hardness  of  7*0,  but  the  cryptocry- 
stalline  varieties  Agate  and  Chalcedony  have  a  hardness  of 
only  6*5  in  some  cases. 


Diamond     . 

10-0 

Garnet  :  Topazolite 

7-0 

Fluor  Spar  . 

4-0 

Demantoid    . 

7-0 

Quartz 

.     6-5—7-0 

Uvarovite 

7-5—8-0 

Opal    . 

.     5-5—6-5 

Olivine 

6-5—7-0 

Corundum  . 

9-0 

Phenakite  . 

7-5—8-0 

Spinel 

.     7-5—8-0 

Dioptase 

5-0 

Chrysoberyl 

8-5 

Idocrase 

6-5 

Calcite 

3-0 

Zircon 

7-5 

Malachite    . 

.     3-5—4-0 

Topaz  .... 

8-0 

Orthoclase  . 

6-0 

Andalusito  , 

7-5 

Microcline  . 

6-0 

Cyanite 

5—6 

Albite 

.     6-0—6-5 

Euclase 

7-5 

Oligoclase  . 

6-0 

Epidote 

6—7 

Labradorite 

6-0 

Axinite 

6-5—7-0 

Pyroxene    . 

5—6 

Prehnite 

6—7 

Spodumene 

.     6-5—7-0 

Tourmaline 

7-0—7-5 

Jadeite 

.     6-5—7-0 

Staurolite    . 

7-0—7-5 

Amphibole  . 

.     5-5—6-0 

Serpentine  . 

3-0 

Crocidolite  . 

.     4-0—4-5 

Sphene 

5-0—5-5 

Beryl  . 

.     7-5—8-0 

Apatite 

5^0 

Cordierite    . 

.     7-0—7-5 

Turquois 

6-0 

Lapis  Lazuli 

5"0  —  5  5 

Gypsum 

2-0 

Garnet  :  Grossular 

.     6-5—7-0 

Amber 

2-0—2-5 

Pyrope  . 

.     6-5—7-5 

Jet      .... 

2-0—2-5 

Almandine 

7-0—7-5 

VII.  CLEAVAGE. 

Minerals  which  occur  in  crystalline  masses  or  in  actual 
crystals  (vide  infra)  have  a  very  definite  internal  arrange- 
ment of  the  molecules  composing  them,  causing  the  mineral 
to  have  different  properties  in  different  directions,  whereas 


PRECIOUS   STONES.  45 

an  amorphous  substance  is  similar  in  all  directions.  One 
of  the  phenomena  noticed  in  crystalline  bodies  is  that  the 
coherence  in  certain  planes  is  weaker  than  in  other  planes. 
There  may  be  one  or  several  such  planes  of  weaker 
cohesion,  and  this  leads  to  the  substance  dividing  along 
such  planes  with  more  or  less  facility  ;  such  a  plane  is 
known  as  a  cleavage  plane,  and  as  it  always  bears  a  definite 
relation  to  the  crystalline  form  of  the  mineral,  it  is  of  great 
use  in  identification  when  the  crystal  faces  are  destroyed, 
or  when  the  form  of  the  crystal  is  very  complex.  From 
the  point  of  view  of  the  gem  cutter,  these  "  cleavages"  are 
of  great  assistance  when  bringing  the  rough  gem  into 
approximately  the  shape  the  finished  stone  is  to  assume. 
This  is  particularly  so  in  the  case  of  the  Diamond,  for  it 
has  four  such  cleavage  planes  which  tend  to  divide  the 
mineral  into  the  form  of  the  regular  octahedron,  from 
which  form  the  commonest  type  of  cut  Diamond,  the  "  bril- 
liant," is  readily  derived.  Adularia,  a  variety  of  Orthoclase 
Felspar,  and  Topaz  are  two  other  precious  stones  which 
show  cleavage  well.  Calcite  has  a  very  perfect  cleavage  in 
three  directions,  tending  to  divide  it  into  rhombs,  a  fact  of 
great  help  in  making  some  of  the  instruments  used  in  the 
optical  examination  of  precious  stones,  such  as  the  polari- 
scope  and  dichroscope. 

A  cleavage  plane  may  be  distinguished  from  an  even 
fracture,  for  the  former  being  a  true  plane,  another  such 
plane  exactly  parallel  to  it  can  be  easily  produced. 

It  must  be  borne  in  mind  that  a  gem  which  possesses 
a  distinct  cleavage  is  more  liable,  other  things  being 
equal,  to  be  broken  or  damaged  by  sudden  changes  of 
temperature. 


46  PEECIOUS   STONES. 

VIII.  CRYSTALLINE  FORM. 

The  greater  number  of  bodies  of  definite  chemical  com- 
position, including  minerals  and  therefore  gems,  occur  in 
"  crystals "  or  are  "  crystalline."  This  leads  us  to  the 
conclusion  that  the  minute  groups  of  chemical  atoms  are 
arranged  in  some  definite  way.  Each  substance  that 
crystallises  has  its  own  definite  geometrical  form ;  this 
might  not  appear  to  be  so  at  first  sight,  for  if  we  took  a 
group  of  crystals  of  Fluor  Spar,  for  instance,  gathered 
together  from  many  different  localities,  the  specimens 
would  seem  at  first  anything  but  similar,  yet  if  we  come  to 
measure  the  angles  between  the  different  planes  or  "faces," 
we  should  find  that  a  good  many  possessed  planes  exactly 
at  right  angles  to  one  another ;  if  the  six  possible  faces  of 
this  kind  were  all  equally  developed,  we  should  see  the 
specimen  was  in  the  form  of  a  perfect  cube — all  the  six 
faces  together  belonging  to  the  "  form  "  of  the  cube;  but 
they  might  not  be  equally  developed  and  the  resulting 
figure  might  be  a  parallelepiped,  or  rectangular  solid  figure 
(with  opposite  sides  equal  necessarily)  having  adjacent 
faces  of  different  sizes.  Still  such  faces  would  be  parallel 
to  the  faces  of  a  perfect  cube  and,  therefore,  would  be, 
crystallographically,  identical.  Again,  amongst  the  Fluor 
Spar  crystals  we  might  find  many  that  showed  the  solid 
angles  of  the  cube  truncated  by  a  plane  having  the  form  of 
an  equilateral  triangle.  Since  parallel  planes  are  identical 
in  a  crystal,  we  might  imagine  these  triangular  faces  moved 
inwards  towards  the  centre  of  the  crystal  until  they  were, 
all  eight  of  them  (one  at  each  corner  of  the  cube),  equally 
distant  from  that  centre ;  there  would  then  obviously  be  no 
face  of  the  cube  left,  but  a  symmetrical  eight-faced  solid 


PRECIOUS   STONES.  47 

figure ;  such  a  form  would  be  a  regular  octahedron.  If  we 
could  bore  through  such  an  octahedron  from  one  of  its 
corners  to  the  diametrically  opposite  corner  in  the  case  of 
each  of  the  three  pairs  of  such  corners,  all  the  bore  holes 
would  pass  through  one  point  at  the  centre.  On  measuring 
the  length  of  the  holes  they  would  be  found  all  equal,  and  each 
one  would  be  at  right  angles  to  the  other  two  holes.  Imagi- 
nary lines  might  be  drawn  down  the  centre  of  each  hole ;  we 
should  then  have  three  lines  of  equal  length,  passing  through 
a  common  point,  and  inclined  to  one  another  at  90°.  Such 
imaginary  lines  would  represent  the  "axes"  of  the  crystal 
of  Fluor  Spar.  It  would  be  noticed  that  each  of  the  faces 
of  the  octahedron  met  the  three  lines  at  points  equally 
distant  from  the  centre  of  the  crystal ;  the  lengths  thus 
cut  off  would  be  the  "  intercepts  "  on  the  axes.  If  other 
faces  of  the  crystal  were  examined  and  the  angles  they 
made  with  one  another  measured,  and  from  these  angles 
the  points  where  these  faces  would  cut  the  axes  were  calcu- 
lated, it  would  be  found  that  the  intercepts  could  be  expressed 
in  whole  numbers ;  for  instance,  a  face  might  cut  one  axis 
at  a  unit  distance  from  the  centre,  and  each  of  the  other  two 
at  twice  this  distance :  the  relation  is  always  a  simple  one. 

An  examination  of  all  the  known  crystallised  bodies 
reveals  the  fact  that  their  crystals  can  be  placed  in  one  of 
six  classes,  known  as  the  six  "  crystallographic  systems." 
They  are  known  as  the  cubic,  hexagonal,  tetragonal,  rhombic, 
monosymmetric  or  monoclinic,  and  the  triclinic.  We  may 
think  of  them  all  with  regard  to  the  relation  of  their  axes. 

The  system  to  which  the  above  example  belongs  is  the 
cubic ;  in  it  there  are  three  axes,  all  at  right  angles,  and  all 
of  equal  length. 

The  hexagonal  system  has  three  equal  axes  inclined  to 


48  PEECIOUS   STONES. 

one  another  at  120°,  intersecting  in  a  point  through  which 

passes  a  fourth  axis  of  length  different  from  the  others. 
The  tetragonal  system  has  two  axes  of  equal  length  at 

right  angles  to  one  another  and  a  third  unequal  axis  at 

right  angles  to  the  other  two. 

The  rhomhic  system  has  three  unequal  axes  all  at  right 

angles. 

The  monosymmetric   system  has  three  axes  of  unequal 

length,  two  of  them  at  right  angles  and  the  third  inclined 

to  the  plane  containing  the  other  two  at  an  angle  other 

than  90°. 

The  triclinic  system  has  three  unequal  axes,  all  inclined 

to  one  another  at  angles  other  than  right  angles. 

The  easiest  way  perhaps  to  get  a  clear  conception  of  the 
simplest  forms  of  each  system  is  to  use  several  pieces  of 
fine   steel   wire;    old   knitting  needles   answer   very   well. 
These   may  be  cut   to  the   lengths  corresponding  to  the 
system  to   be  represented ;  for  instance,  for    the  rhombic 
system  we  might  have  one  piece  3  inches  long,  one  piece 
2J  inches  and  another  1^    inches  in  length.     These  can 
now  be  run  through  an  indiarubber  ball  of  about  1  inch 
diameter,  taking  care  to  keep  them  as  near  the  centre  of 
the  ball  as  possible  and  at  right  angles  to  one  another. 
If  the  ball  be  now  covered  over  with  moist  pipeclay  moulded 
into  an  eight-faced  solid  figure  whose  corners  coincide  with 
the  tips  of  the  wires,  a  rhombic  pyramid  will  be  produced. 
If  a  set  of  the  pyramids  belonging  to  the  six  systems  of 
crystals  be  made  in  this  way,  a  general  conception  of  their 
form  is  obtained. 

It  must  be  borne  in  mind  that  the  external  form  of  a 
crystal  is  by  no  means  its  most  important  phenomenon,  for 
with  this  external  form  is  associated  a  definite  internal 


PEECIOUS   STONES.  49 

structure   on   which    depend  so   many   of    the   properties 
already  mentioned. 

In  relation  to  precious  stones,  crystallography  is  chiefly  of 
importance  in  the  case  of  uncut  gems,  or  in  the  cutting  of  a 
stone ;  but  a  knowledge  of  the  properties  dependent  on  the 
internal  structure  aids  very  greatly  in  the  identification  of  a 
cut  specimen  (cf.  Physical  Properties  Dependent  on  Light). 

When  a  mineral  only  shows  the  internal  structure  with- 
out any  definite  external  crystal  forms  it  is  said  to  be 
"  crystalline."  When  the  external  form  is  developed  the 
internal  arrangement  of  the  molecules  is  always  present, 
and  the  mineral  is  then  said  to  be  "  crystallised." 

Crystals  deposited  from  an  ordinary  aqueous  solution  are 
usually  found  to  have  started  their  growth  from  some  pre- 
existing solid  body ;  the  point  from  which  this  growth 
commences  is  known  as  the  point  of  attachment.  Many  of 
the  beautiful  groups  of  Kock  Crystal  from  the  Alps  show 
this  very  clearly.  Such  crystals  are  necessarily  imperfect 
in  outline  at  this  point. 

When  crystals  are  deposited  during  the  cooling  of  rocks 
undergoing  hydro-thermal  metamorphism,  two  modes  of 
occurrence  are  to  be  noticed.  If  the  mineral  in  question  is 
one  which  for  some  reason  or  another  crystallises  out 
before  the  majority  of  its  associated  minerals,  its  crystals 
are  very  likely  to  be  perfectly  developed  all  round — they 
have  the  characteristic  external  shape  .of  the  crystals 
of  that  mineral;  they  are  then  said  to  be  " idiomorphic." 
Crystals  which  during  their  deposition  are,  so  to  speak, 
crowded  against  other  crystals,  may  mutually  compress  one 
another  so  that  in  a  large  part  their  external  form  is  not  the 
characteristic  one;  in  such  a  case  they  are  " allotriomorphic." 

p.s.  E 


CHAPTEK   IV. 

THE    CUTTING    OF    GEMS. 

IT  is  somewhat  doubtful  at  what  period  the  true  cutting 
of  gems  was  first  practised.  There  is  no  doubt  that  from 
very  early  times  precious  stones  were  polished,  often  into 
curved  forms,  often  simply  on  the  natural  crystal  faces,  to 
remove  the  cloudy  films  present.  If  we  regard  cutting  as 
the  production  on  the  gem  of  surfaces,  usually  plane,  with 
the  removal  of  a  considerable  amount  of  the  material,  we 
may  regard  the  art  as  dating  before  1475,  by  which  time 
Louis  de  Berquem  performed  the  operation.  Charles  the 
Bold  sent  him  three  Diamonds  to  cut.  The  first  one  to 
be  actually  cut  was  a  large  pyramidal  stone,  about  f  inch 
on  the  edge.  It  was  cut  into  a  regular  pyramid,  whose 
apex  was  modified  by  a  four-rayed  star,  each  ray  being  of 
two  triangular  facets.  It  was  set  with  three  large  Balas 
Eubies  and  four  pearls,  as  a  pendant.  It  was  taken  as 
plunder  from  the  tent  of  Charles  at  Granson  (1475)  by  a 
common  soldier,  who  threw  it  away  once,  but  afterwards 
recovered  it,  and  sold  it  to  a  priest,  who  afterwards  sold  it 
for  ten  times  what  he  gave  for  it  to  the  authorities  of  his 
district ;  thence  it  passed  to  the  Bernese  Government,  who 
sold  it,  with  other  jewels,  to  Jacob  Fugger  for  47,000 
florins.  Fugger's  great-nephew  made  an  accurate  full-size 
drawing  of  the  pendant,  which  is  reproduced  in  the  Bib. 


PEECIOUS    STONES.  51 

Imperialis  of  Lambeccius.  The  jewel  was  afterwards  sold 
to  Henry  VIII. ,  and  passed  to  Mary,  who  made  a  present 
of  it  to  Philip.  It  is  possible  it  is  still  amongst  the  Spanish 
jewels  in  a  re-cut  state.  Fugger's  drawing  is  reproduced  in 
King's  "  Precious  Stones,"  with  many  interesting  facts 
about  the  jewel. 

Numerous  jewels  of  the  sixteenth  century  show  the 
original  style  of  cutting  introduced  by  de  Berquem. 
Kentwaur,  in  1562,  mentions  two  types  of  cutting,  the 
"point"  and  the  "  table."  The  former  was  simply  the 
natural  octahedron,  with  the  faces  reduced  to  a  perfectly 
regular  form,  and  polished ;  but  the  latter  had  one  apex 
ground  down  till  the  flat  surface  produced  was  equal  in 
width  to  the  two  adjacent  sloping  facets  added  together, 
and  the  opposite  apex  was  likewise  ground  down  to  a  plane, 
but  of  smaller  extent,  and  all  the  surfaces  polished  (Fig.  4). 
In  the  case  of  a  thin  stone,  the  portion  below  the  setting 
consisted  of  a  large  plane,  while  the  upper  portion  was  cut 
as  the  above  table. 

The  "  rose  "  (p.  55)  was  produced  in  the  middle  of  the 
seventeenth  century,  and  by  1665  the  famous  Mogul  was  cut 
into  a  high-crowned  rose  of  280  carats  by  the  Venetian 
jeweller  Borghis.  The  "brilliant"  cut  was  discovered  by 
another  Venetian,  Peruzzi,  towards  the  end  of  the  seven- 
teenth century,  from  experiments  on  coloured  stones.  This 
was  similar  in  general  form  to  the  older  table-cut  stone,  but 
was  worked  in  a  more  elaborate  fashion,  having  thirty-two 
facets  above  and  twenty-four  below  the  "  girdle,"  besides 
the  "  table  "  and  "  collet,"  or  fifty-eight  facets  in  all. 

Louis  de  Berquem's  .essential  discovery  was  the  fact 
that  one  Diamond  will  abrade  another  when  the  two  are 

K  2 


52 


PEECIOUS   STONES. 


FIG.  4.— The  FIG.  5.— Step- 

Table,  cut. 


FIG.  6.— The 
Eose. 


FIG.  7. — Brilliant- 
cut. 


IG>  s. — The  Pitt  or 
Regent  Diamond. 


PRECIOUS   STONES.  53 

rubbed  together.  To  Peruzzi  would  seem  to  belong  the 
honour  of  discovering  the  principle  of  modifying  the  back 
of  the  stone  so  as  to  bring  out  the  full  brilliance  of  the 
specimen.  As  pointed  out  when  dealing  with  light,  this 
brilliance  depends  jointly  on  refraction  and  repeated  internal 
reflection. 

By  far  the  most  important  type  of  cutting  is  that  called 
the  brilliant.  In  this  form  the  greatest  circumference  of 
the  stone  is  called  the  "girdle";  the  portion  lying  above 
the  girdle  is  the  "crown,"  and  that  below  is  the  "culasse." 
The  crown  terminates  in  a  large  plane  called  the  table 
(a,  Fig.  7) .  Meeting  the  table  in  an  edge  are  eight  triangular 
facets  called  the  "  star  facets  "  (6,  Fig.  7) ;  meeting  the  girdle 
in  an  edge  are  sixteen  upper  "  skill  facets  "  (c,  Fig.  7) ; 
and  between  the  star  facets  and  the  upper  skill  facets  are 
eight  lozeng'e-shaped  facets  known  as  "  bezils  "  (d,  Fig.  7). 
Below  the  girdle,  that  is  on  the  culasse,  are  sixteen  tri- 
angular facets  meeting  the  girdle  in  an  edge.  These  are 
the  lower  "skill  facets"  (/,  Fig.  7);  and  running  from 
them  to  the  lowest  portion  of  the  stone  are  eight  facets,  with 
five  sides  each,  called  the  "pavilions"  (Y/,  Fig.  7).  The 
lowest  portion  of  the  stone  is  a  small  plane  called  the 
"  collet  "  (/i,  Fig.  7).  Sometimes  the  upper  and  lower  skill 
facets  are  collectively  referred  to  as  "  cross  facets."  There 
are  thus  thirty-three  planes  in  the  crown,  and  twenty-five 
in  the  culasse.  The  table  and  collet  are  both  parallel  to 
the  plane  of  the  girdle. 

There  is  a  general  proportion  in  the  finished  stone  which 
has  become  by  the  experience  of  generations  of  cutters  to 
be  regarded  as  a  standard,  because  a  stone  so  proportioned 
is  found  to  give  the  greatest  brilliancy.  Thus  if  the 


54  PKECIOUS   STONES. 

diameter  of  the  collet  be  taken  as  unity,  the  girdle  should 
be  nine  units  in  diameter,  and  the  table  five  ;  also  the 
vertical  distance  from  table  to  girdle  should  be  one-half 
the  vertical  distance  of  the  collet  from  the  girdle.  These 
proportions  give  the  outline  shown  in  Fig.  7,  and  as  will 
be  seen  from  Fig.  3,  the  angles  thus  formed  are  eminently 
adapted  to  repeatedly  reflect  the  light  within  the  stone. 
The  exact  finished  form  of  the  stone  is  by  no  means  fixed, 
but  is  modified  by  the  cutter  to  suit  the  rough  gem  he  is 
dealing  with,  so  as  to  sacrifice  as  little  material  as  is 
consistent  with  giving  a  good  result.  In  the  case  of 
colourless  and  transparent  stones  the  proportions  given 
above  are  adhered  to  more  or  less  closely ;  but  the  plan 
of  the  stone  may  be  considerably  modified.  Thus  it  may 
be  generally  circular,  as  in  Fig.  7,  or  square  or  oblong, 
as  in  the  Pitt  or  Eegent  Diamond  (Fig.  8),  or  triangular, 
etc.  Again,  a  coloured  stone  is  usually  cut  in  a  rather  more 
shallow  form;  the  deeper  the  colour,  usually,  the  thinner 
the  stone.  If  the  stone  were  of  the  proportion  of  a  colourless 
gem  the  tint  might  be  so  deep  as  to  lose  a  great  deal  of 
its  beauty. 

The  presence  of  a  flaw  or  other  imperfection  may  con- 
siderably modify  the  form  given  to  the  finished  stone  ;  as 
a  rule  the  English  cutters  prefer  to  have  the  gem  perfect 
technically  even  at  the  sacrifice  of  a  good  deal  of  weight,  and 
hence  flaws  are  either  removed  altogether,  or  at  least  the 
stone  is  so  cut  that  the  flaw  comes  in  the  girdle,  where  it  is 
not  so  conspicuous.  The  slightest  imperfection  in  the  region 
of  the  collet  has  a  very  great  influence  on  the  appearance 
of  the  gem,  as  it  is  reflected  again  and  again,  and  thus  seem- 
ingly magnified.  The  triple- cut  brilliant  form  is  only  given 


PBECIOUS  STONES.  55 

to  larger  stones  of  good  quality,  smaller  stones  being  cut  in 
some  of  the  many  modifications  of  the  brilliant  pattern, 
such  as  the  double  brilliant,  or  even  more  simple  forms. 
An  English-cut  stone  can  often  be  distinguished  by  the 
greater  accuracy  given  to  the  angles  of  the  facets,  so  that 
the  resulting  gem  is  exactly  symmetrical. 

Among  the  many  other  forms  into  which  gems  are  cut,  a 
few  may  be  mentioned :  for  transparent  stones,  besides  the 
brilliant-cut  there  is  the  "  step-cut  "  ;  in  this  the  facets  are 
elongated,  the  longer  edges  being  parallel  so  as  to  form  a 
series  of  steps.  The  crown  may  have  two  or  three  steps 
and  the  culasse  five  or  six  or  more ;  table  and  collet  are 
formed  as  in  the  brilliant.  A  step -cut  stone  may  be  square 
or  six  sided,  etc.,  just  as  a  brilliant;  this  form  is  shown  in 
the  square  type  in  Fig.  5.  Two  older  forms  of  cut  have 
already  been  referred  to:  the  "point,"  in  which  the  octa- 
hedral crystal  faces,  or  the  octahedral  cleavage  planes  were 
simply  rendered  symmetrical  in  outline  and  polished,  and  the 
"  table-cut,"  in  which  a  table  and  collet  were  formed  (Fig.  4). 
Another  type  is  the  "  rose."  In  this  the  gem  is  worked 
into  a  series  of,  usually,  triangular  facets,  arranged  in  two 
series,  an  upper  series  forming  the  crown  or  star,  and  a 
lower  series,  that  called  the  teeth ;  the  under  surface  is 
a  simple  plane  (Fig.  6).  More  rarely  stones  are  cut  into 
a  general  pear  shape,  worked  all  over  with  small  triangular 
facets,  "  briolette ;  "  or  into  a  "  rosette,"  which  has  the 
form  of  two  rose-cut  stones  joined  together  by  their  large 
plane  surfaces  ;  occasionally  a  very  thin  stone  is  cut  as 
a  "  half-brilliant,"  which  is  similar  to  the  crown  only  of  an 
ordinary  brilliant,  the  lower  part  of  the  stone  consisting 
of  a  large  plane,  as  in  the  rose. 


56  PBECIOUS  STONES. 

Garnets  are  frequently  cut  "  en  cabochon.'"  In  this  form 
the  upper  surface  is  a  low  dome,  convex  towards  the  eye  ;  the 
under  surface  is  flat,  or,  in  the  case  of  very  intensely  coloured 
stones,  concave,  so  that  the  stone  in  section  would  show  a 
parallel  curved  outline ;  or  the  concavity  may  be  such  as  to 
leave  the  stone  thicker  at  the  centre  and  thinner  at  the  edges. 
Barely,  the  upper  convex  surface  is  worked  in  small  facets 
around  its  margin.  Turquois  is  often  cut  en  cabochon  ; 
Chrysoprase  may  be  cut  so,  too,  but  more  often  it  is  given  a 
lower  curve,  "  Goutte  de  suif"  being  the  name  then  used. 

Many  of  the  coloured  gems  as  Topaz,  Sapphire,  Euby, 
Emerald,  Garnet,  Peridot,  Amethyst,  Cairngorm,  etc.,  are 
frequently  step-cut,  though  they  may  be  formed  into  bril- 
liants, and  are,  in  many  cases,  so  cut.  The  Chrysoberyl  is 
usually  cut  as  a  brilliant ;  colourless  Corundum  is  usually 
step-cut ;  most  of  the  opaque  gems  are  cut  either  en  cabochon 
or  as  the  "  tallow-drops  "  above  referred  to  ;  very  often  the 
margin  in  Chrysoprase  is  worked  with  one  or  two  rows  of 
small  triangular  facets.  Cat's-eye  is  usually  cut  en  cabochon, 
and  the  finished  stone  must  be  so  arranged  as  to  have  a 
definite  relation  to  the  internal  structure  of  the  gem,  to 
show  its  full  beauty.  Moonstone  and  Labradorite  mast  also 
have  a  definite  relation  to  the  crystal  structure  to  bring  out 
the  best  effect. 

In  the  actual  cutting  of  precious  stones  in  general,  a 
careful  study  of  the  rough  stone  has  first  to  be  made  to 
determine  in  what  direction  it  can  best  be  cut  so  as  to 
leave  as  large  a  finished  gem  as  possible,  free  from  imper- 
fections ;  this  having  been  decided  on,  these  imperfections 
are  removed  and  the  stone  brought  to  approximately  the 
desired  shape  by  methods  varying  with  the  mineral  in 


PEECIOUS  STONES.  57 

hand.  In  the  case  of  the  Diamond,  unless  the  rough  stone 
is  of  the  octahedral  form  already,  cleavage  is  first  made  use 
of  as  far  as  possible.  In  cleaving  a  Diamond  the  stone  is 
cemented  firmly  to  the  end  of  a  support  in  such  a  position 
that  when  the  support  is  fixed  on  the  bench  so  as  to  be 
vertical,  the  cleavage  plane  to  be  attacked  will  also  be 
vertical.  The  support  is  then  put  in  position,  and  means 
taken  for  ensuring  the  collection  of  any  fragments.  A  steel 
blade  is  now  placed  in  the  cleavage  plane  at  the  desired 
point  and  a  sharp  tap  delivered  on  the  blade  by  a  rod  held 
in  the  right  hand ;  by  repeating  this  process  a  cleavage 
octahedron  free  from  flaws  is  produced.  The  cement  used 
is  a  solution  of  shellac  in  turpentine,  thickened  with  very 
fine  brick-dust.  Often  before  applying  the  cleaving  blade  a 
fine  groove  is  cut  in  the  "  trace  "  of  the  cleavage  plane  by 
means  of  another  Diamond.  The  art  of  cleaving  Diamond 
.is  said  to  have  been  known  in  the  East  from  ancient  times  ; 
it  seems  to  have  been  discovered  independently  by  Wollaston, 
although  De  Boot  (1609),  speaking  of  the  Diamond,  says 
he  knew  a  physician  who  could,  "without  the  aid  of  any 
instrument  or  material,  other  than  those  furnished  by  the 
human  body,  divide  it  into  fine  scales  like  a  piece  of  talc." 
However,  Dr.  Wollaston  turned  his  discovery  to  good  advan- 
tage by  buying  up  mis-shapen  Diamonds  that  the  jewellers 
had  considered  not  worth  the  enormous  labour  of  grinding 
into  shape,  and,  by  cleaving  them,  he  reduced  them  to  a 
form  easily  worked  on. 

After  the  cleaving  has  been  effected  by  one  workman, 
the  stone  is  handed  to  another,  who  is  known  as  a  bruter. 
Tbe  operation  he  performs  is  the  brutage,  or  bruting. 
This  operation  is  the  outcome  of  de  Berquem's  discovery 


58  PEECIOUS  STONES. 

that  when  one  Diamond  is  rubbed  on  another  each  is 
abraded ;  it  is  made  use  of  to  still  more  nearly  approximate 
the  stone  to  its  desired  form.  The  stone  is  cemented  to  the 
end  of  a  wooden  holder  about  a  foot  long,  and  two  stones 
are  wrought  simultaneously  by  grasping  the  two  holders 
and  rubbing  the  stones  together  in  the  desired  direction 
over  a  wooden  trough,  into  which  the  fragments  and  dust 
fall,  and  in  which  they  are  separated  into  larger  and  smaller 
particles  by  a  fine  sieve.  In  bruting,  care  must  be  taken  not 
to  overheat  the  stone  by  the  friction,  or  a  scaly  appearance 
may  be  produced  in  the  interior  of  the  gem.  When  the 
bruting  is  completed  the  surfaces  have  somewhat  the  aspect 
of  ground  glass.  The  table  and  collet  are  the  most  impor- 
tant faces  to  be  dealt  with  at  this  stage,  and  entail  the 
greatest  amount  of  work,  as  there  is  no  cleavage  that  can 
assist  in  roughing  out  these  planes  ;  working  in  a  plane 
normal  to  an  axis  of  the  octahedron  five-ninths  of  the 
upper  pyramid  must  be  removed  to  produce  the  finished 
table,  and  at  the  other  end  of  the  same  axis  one-ninth 
of  the  lower  pyramid  for  the  collet. 

In  Amsterdam  the  Diamonds  are  sometimes  slit  by  a  disc 
of  thin  metal  revolving  at  high  speed,  and  dressed  on  its 
edge  by  diamond-dust  and  olive  oil.  This  method  allows  of 
a  slice  being  taken  off  in  any  direction  desired,  but  the 
process  is  extremely  slow,  taking  many  days  to  accomplish ; 
and  it  is  stated  that  the  resulting  finished  stone  is  inferior 
in  quality  to  one  that  has  been  cleaved. 

Sometimes  the  larger  planes  are  roughed  out  by  working 
the  stone  in  a  high-speed  lathe. 

When  the  bruting  is  completed,  there  yet  remains  much 
work  to  be  done,  for  the  smaller  facets  have  to  be  wrought 


PEECIOUS   STONES.  59 

and  the  whole  gem  polished ;  this  is  done  by  the  polisher. 
But  first  it  must  be  mounted  on  a  suitable  holder  by  the 
solderer ;  small  brass  cups,  known  as  "  dops,"  of  one  or 
two  inches  in  diameter,  and  having  a  short  stalk  attached, 
are  heated  in  a  Bunsen  flame  and  filled  with  a  solder 
composed  of  one  part  of  tin  to  two  parts  of  lead,  similar 
to  the  solder  plumbers  use  for  wiped  joints  in  lead  pipes. 
This  alloy  melts  at  about  441°  F.  or  227°  C.,  and  has  the 
property  of  being  plastic  at  considerably  below  its  melting 
point.  When  the  solder  has  attained  the  plastic  state  by 
sufficient  heating,  and  has  been  worked  up  into  a  cone  pro- 
jecting from  the  hollow  of  the  cup,  the  stone  is  embedded 
in  the  metal  at  the  apex  of  the  cone  in  such  a  way  that  only 
the  part  of  the  gem  to  be  immediately  worked  on  is 
exposed  ;  on  cooling  down  the  solder  contracts  considerably 
and  grips  the  stone  very  firmly.  Soldering,  like  other 
operations  in  gem  cutting,  requires  great  dexterity  and 
experience,  as  the  stone  must  be  fixed  at  the  correct 
angle,  so  that  its  position  can  be  known  by  the  position 
of  the  holder,  and  further,  in  the  case  of  the  Diamond  (or 
other  cleavable  gems),  the  alternate  contraction  and  expan- 
sion from  heating  and  cooling  may  cause  flaws  if  the 
operation  is  not  done  very  skilfully. 

In  some  cases  a  split  clamp,  tightened  by  a  thumb-screw, 
is  used  to  hold  the  stones,  instead  of  their  being  soldered 
into  the  dops. 

The  dop,  or  its  substitute,  is  now  mounted  in  a  clamp 
which  in  its  simple  form  consists  of  a  bar  rather  less  than 
a  foot  in  length,  having  a  slot  at  one  end ;  the  parts  of  the 
clamp  on  either  side  of  the  slot  can  be  brought  together  by 
a  bolt  and  nut  so  that  the  peg  of  the  dop  may  be  firmly 


60  PRECIOUS  STONES. 

held  there ;  the  other  end  of  the  clamp  is  formed  into  two 
vertical  legs  or  supports  of  such  a  height  that  when  resting 
on  the  table,  with  the  bar  of  the  clamp  horizontal  and  the 
dop  fixed,  the  gem  mounted  on  the  dop  is  about  an  inch 
above  the  table.     The  clamps  are  made  of  iron,  and  when 
in  use  are  further  weighted,  as  the  need  occurs,  with  lead 
weights.     In  the  case  of  the  Diamond,  grinding  and  polish- 
ing occur  simultaneously,  and  are  performed  on  a  rapidly 
rotating  disc  of  iron  called  a  "  skief "  or  "lap."      This  lap 
is  a  wheel  of  about  twelve  inches  diameter  and  one  inch 
thick,  mounted  on  a  steel  shaft  running  on  pivot  bearings ; 
the  wheel  is  of  porous  cast-iron,  and  it  is  mounted  so  as  to 
rotate  in  a  horizontal  plane  an  inch  or  so  above  the  level 
of  the  bench.    The  rate  of  rotation  is  always  high,  and  the 
harder   the  stone  under  treatment  the  greater  the  speed 
necessary  to  obtain  a  cutting  effect.    When  the  speed  is  high 
enough,  a  gem  may  be  abraded  by  a  substance  of  its  own 
degree  of  hardness,  or  even  one  of  a  lower  degree,  though, 
of  course,  the  harder  the  abrading  agent  in  comparison  to 
the  gem,  the  more  rapid  the  progress  with  the  work.     The 
usual  speed  may  be  taken  as  2,000  to  3,000  revolutions  per 
minute,  which  gives  a  peripheral  cutting  velocity  of,  roughly, 
100  to  150  feet  per  second,  or  say  75  to  100  miles  per  hour. 
Power  is  applied  by  steam,  gas,  water,  or  from  an  electro- 
motor, and  the  spindle  is  driven  by  a  small  pulley  running 
below  the  bench.     The  abrading  material  in  the  case  of 
Diamond  is  always  the  powder  of  the  same  mineral,  as  no 
harder  substance  is  available  ;  this  is  naturally  expensive, 
hence  the  precaution  taken  to  save  all  dust  from  the  process 
of  bruling.    In  the  cleaving,  too,  such  fragments  as  are  too 
small  to  be  cut  for  gem  use  are  saved,  and  are  later  crushed 


PEECIOUS  STONES.  61 

in  a  steel  mortar  furnished  with  a  well-fitting  cylindrical 
pestle  of  steel,  the  dust  being  used  in  the  same  way  as  that 
from  bruting.  The  impure  variety  of  Diamond,  called  Bort, 
is  also  extensively  used  and  also  the  finely  granular  opaque 
variety,  Carbonado.  Bort  is  harder  than  the  pure  crystal- 
lised variety,  and  Carbonado  is  as  hard  or  harder,  and  is  also 
less  brittle  than  the  pure  Diamond. 

The  abrasive  agent  is  mixed  with  a  little  olive  oil  in  a 
capsule  and  a  small  quantity  of  the  mixture  applied  to  the 
upper  surface  of  the  lap  or  skief.  The  clamp  with  the  dop 
in  position  is  then  lowered  so  that  the  gem  rests  on  the  lap. 
The  position  must,  of  course,  be  accurately  adjusted  to 
grind  the  stone  in  the  desired  plane;  usually  one  operator 
manipulates  four  dops,  placed  equally  distant  round  the 
lap  so  as  to  distribute  the  pressure  evenly.  As  before  men- 
tioned, the  clamps  are  weighted  with  lead  weights  to  give 
sufficient  pressure,  without  which  the  work  would  progress 
much  more  slowly.  With  a  given  weight  it  is  obvious  that 
the  pressure  on  a  given  area  will  be  less  with  a  large  facet 
than  with  a  small,  since  the  same  total  force  is  applied 
over  a  larger  area  in  the  former  case  than  in  the  latter ; 
hence  to  maintain  an  even  pressure  the  weights  must  be 
altered.  The  weights  applied  vary  from  2  to  30  Ibs. 

As  an  instance  of  the  importance  of  having  a  proper 
speed,  it  may  be  recalled  that  in  the  cutting  of  the 
Koh-i-noor  the  work  was  being  done  with  the  wheel  at 
2,400  revolutions  per  minute.  When  the  cutters  came  to 
one  part,  however,  no  progress  seemed  to  be  made ; 
greater  pressure  was  applied,  with  the  result  that  particles 
of  the  iron  disc,  mixed  with  oil  and  diamond-powder, 
became  ignited,  and  then  the  solder  began  to  melt.  At  one 


62  PBECIOUS   STONES. 

point  after  six  hours'  work  no  effect  seemed  to  have  resulted, 
but  on  increasing  the  speed  to  3,000  re  volutions  per  minute 
the  grinding  proceeded  satisfactorily,  though  the  total 
time  spent  in  cutting  it  was  456  hours  ;  it  was  found,  too, 
in  this  case  that  they  were  cutting  across  the  angle  of 
meeting  of  two  cleavage  planes,  or  "  across  the  grain  "  as 
it  is  expressed.  This  is  then  also  a  good  instance  of  the 
importance  of  grinding  in  the  right  direction,  for  the 
hardness  varies.  It  is  found  that  the  directions  of 
least  hardness  are  in  lines  between  the  centres  of  oppo- 
site octahedral  faces — that  is,  the  cutting  must  not 
take  the  direction  of  the  crystallographic  axis  in  the 
Diamond. 

The  abrading  material  quickly  works  its  way  into  the 
pores  of  the  cast-iron  disc,  hence  the  disc  does  not  become 
worn  away  so  quickly  as  one  might  expect. 

When  one  facet  has  become  ground  down  to  its  proper 
shape  and  size  and  has  received  as  high  a  polish  as  possible, 
the  dop  is  altered  in  the  holder  so  as  to  bring  the  stone  into 
position  for  another  facet  to  be  ground.  When  as  many  of 
the  required  planes  have  been  formed  as  the  position  of  the 
stone  in  the  solder  will  allow,  the  dop  is  returned  to  the 
solderer  to  have  the  stone  re-set  at  another  angle.  Fre- 
quently the  dops  are  so  hot  that  they  cannot  be  conveniently 
handled,  so  wooden  holders  are  provided ;  they  are  of  a 
shape  similar  to  a  dumbbell  with  a  hollow  down  the  handle, 
into  which  the  peg  of  the  dop  is  placed. 

To  keep  the  stone  from  becoming  overheated  the  dop  is 
from  time  to  time  placed  in  water  to  cool. 

More  recently  clamps  have  been  used  fitted  with  divided 
arcs,  so  that  the  stone  may  be  placed  on  the  lap  at  exactly 


PEEOIOUS  STONES.  63 

the  required  angle.  In  this  way  much  more  precise  work  is 
possible. 

When  all  the  facets  have  been  polished,  the  stone  is 
cleaned  by  treatment  with  a  softer  material,  such  as  bone 
ash  or  tripolite. 

The  treatment  of  softer  stones  is  somewhat  different. 
Some  of  them,  as  Topaz  and,  to  a  lesser  degree,  Beryl  may 
be  partly  formed  by  cleavage,  but  in  most  cases  the  form  is 
given  entirely  by  grinding.  For  the  varieties  of  Corundum, 
for  Chrysoberyl,  Emerald  and  other  hard  stones,  the  lap  is 
made  of  iron,  copper,  tin,  pewter,  or  lead  :  usually  the 
harder  the  gem,  the  harder  the  disc  used.  The  abrasive 
material  is  now  often  Diamond,  for  though  this  means  a 
greater  cost  in  material,  there  may  be  a  greater  saving  in 
total  cost  of  the  work  from  the  greater  rapidity  of  grinding : 
the  coarser  varieties  of  Corundum  known  as  Emery  are 
also  used,  and  now  the  artificially  prepared  compound  of 
carbon  and  silicon,  called  carborundum,  is  extensively 
employed.  Carborundum  is  made  by  the  treatment  of 
sand  and  coke  in  the  arc  of  an  electric  furnace,  and  can  be 
produced  cheaply  in  considerable  quantity;  in  commerce  it 
is  found  in  brilliant  hexagonal  crystals  of  a  rich  yellow 
colour,  often  merging  into  the  blue  known  as  "  electric 
blue,"  giving  the  crystals  very  much  the  appearance  of 
the  Haematite  crystals  from  Elba.  Carborundum  has  the 
further  advantage  of  being  very  hard — much  harder  than  the 
Sapphire — and  yet  easily  reducible  to  powder  on  account  of 
its  brittleness.  The  softer  abrasives  are  mixed  with  water 
instead  of  with  oil ;  sometimes  powdered  Garnet  and  Topaz 
are  used. 

The  gem  is  cemented  to  the  end  of  a  holder  of  wood  or 


64  PRECIOUS  STONES. 

ivory  about  five  or  six  inches  long,  and  this  holder  is 
steadied  against  a  rest  fixed  near  the  right-hand  side  of  the 
lap ;  the  wheel  is  in  some  cases  rotated  by  hand,  but  more 
often  by  power,  as  in  Diamond  grinding.  The  stone  is  first 
roughly  ground  to  shape  and  then  the  facets  are  ground  on ; 
a  close  watch  has  to  be  kept  for  the  appearance  of  any 
small  cracks  in  the  work,  which  if  not  carefully  dealt  with 
are  apt  to  extend  and  spoil  the  stone. 

In  grinding  the  relatively  softer  gems,  the  abrading 
material,  as  in  grinding  the  Diamond,  presses  its  way  into 
the  metal  of  the  lap. 

The  stone  is  now  handed  to  another  worker  to  be 
polished.  This  process  consists  of  carefully  following  the 
previous  work  and  rendering  the  facets  as  smooth  and 
bright  as  possible.  The  lap  used  is  similar  to  the  grinding 
lap  in  type,  but  is  usually  of  softer  material,  in  the  case  of 
softer  stones  often  of  wood,  covered  with  leather  or  paper, 
on  which  the  polishing  material  is  smeared.  When  laps  of 
copper,  lead,  or  pewter  are  used  the  surface  is  finely 
scratched  with  a  piece  of  sandstone,  so  as  to  give  minute 
grooves,  arranged  similarly  to  the  large  grooves  on  a  mill- 
stone; this  has  the  effect  of  evenly  distributing  the  polishing 
material.  Several  substances  are  used  in  polishing:  rouge 
and  putty-powder  (respectively  oxides  of  iron  and  tin), 
rotten  stone,  fine  pumice,  tripolite  and  bole  being  amongst 
these.  Tripolite  is  mixed  with  sulphuric  acid  for  use,  the 
others  are  mixed  with  water.  All  these  substances  must 
be  in  the  form  of  the  very  finest  powder,  or  the  work  will 
not  acquire  the  high  polish  desired. 

When  a  large  portion  of  rough  material  lias  to  be  removed 
before  grinding  can  be  commenced,  it  is  usually  effected  by 


PKECIOUS   STONES.  65 

slitting  with  a  metal  disc,  as  described  in  dealing  with  the 
slitting  of  Diamonds,  powdered  Diamond  mixed  with  olive 
oil  being  used  to  make  the  disc  cut  the  harder  stones, 
while  for  the  softer,  Emery  powder  and  water  may  be 
applied  to  the  somewhat  roughened  edge.  The  natives  of 
Ceylon  used  a  fine  wire  strung  on  a  bow  and  dressed  with 
the  cutting  powder  to  slit  precious  stones. 

In  cutting  stones  en  cabochon  the  operator  holds  the  little 
handle  on  which  the  gem  is  mounted  and  keeps  it  con- 
stantly moving  in  position,  especially  as  the  work  nears 
completion,  so  as  to  give  a  smoothly-rounded  form.  The 
smaller  Garnets  are  fashioned  on  a  fine  sandstone  disc, 
dressed  with  Emery  powder  and  olive  oil. 

The  cutting  of  Agates,  Amethyst,  Opal,  Topaz,  Jasper  and 
other  stones  which  are  relatively  softer  and  more  plentiful, 
is  largely  done  at  Birkenfeld,  on  the  Nahe,  lying  to  the 
west  of  the  Ehine,  close  to  the  French  frontier.  Here  may 
yet  be  seen  many  of  the  older  methods  still  in  use.  The 
work  is  carried  on  in  small  huts  adjacent  to  streams  which 
provide  the  power  to  drive  the  water-wheels,  which  in  turn 
drive  three  or  four  grindstones  of  about  four  feet  in  dia- 
meter ;  the  grindstones  are  so  placed  that  their  axles  are 
only  a  foot  above  the  floor  level,  while  the  lowest  part  of 
the  stone  dips  into  the  stream  below,  and  thus  the  stone  is 
kept  constantly  wet.  The  workmen  lie  prone  on  low 
wooden  supports,  and  hold  their  work  a  little  above  the 
level  of  the  floor.  In  spite  of  the  stones  being  kept  moist, 
a  great  deal  of  dust,  consisting  of  sharp,  angular  mineral 
fragments,  is  thrown  off,  and  consequently  inhaled,  giving 
rise  to  great  irritation  in  the  lungs,  and  paving  the  way 
for  consumption,  which,  having  once  been  introduced, 

p.s.  F 


66  PEECIOUS   STONES. 

frequently  attacks  and  carries  off  the  workers  in  their 
prime. 

Gem  stones  may  be  bored  by  a  fine  diamond-tipped 
drill,  or  by  a  small  steel  drill  dressed  with  diamond-dust 
and  olive  oil,  and  made  to  rotate  at  a  high  speed. 

In  the  processes  of  cutting  and  polishing,  a  rough  gem 
will  lose  50  per  cent,  of  its  weight,  or  more  if  a  large  stone, 
or  40  per  cent.,  more  or  less,  in  small  stones;  when  the 
rough  gem  is  nearly  the  form  required,  as  in  the  case  of  an 
octahedral  Diamond,  the  loss  may  be  considerably  less. 


CHAPTEE  V. 

1       IMITATION    GEMS    AND    THE    ARTIFICIAL    PRODUCTION    OF 
PRECIOUS    STONES. 

THE  art  of  making  imitation  gem-stones,  although 
brought  to  a  very  high  standard  of  perfection  to-day,  is  by 
no  means  a  thing  of  yesterday.  It  is  an  art  that  takes  us 
back  far  into  the  remote  past,  almost  to  the  verge  of  pre- 
historic times,  when  man  first  began  to  think  of  personal 
adornment. 

The  early  Egyptians  made  imitations — imitations  that 
may  have  been  used  as  jewels,  or  simply  as  copies  of  rare 
gems.  For  what  purpose  they  were  made  is  not  known 
with  certainty.  In  the  tombs  of  upper  Egypt  we  find 
"  pastes  "  that  carry  us  back  to  the  earlier  dynasties,  nearly 
2,000  B.C.  Egypt  was  even  then  in  a  high  state  of  civilisa- 
tion. Later  we  find  the  Greeks,  Etruscans,  and  Komans 
making  them.  Pliny  mentions  the  "  glass  gems  from  the 
rings  of  the  multitude  "  ;  and  again  he  says,  "  that  so  well 
made  were  they  of  lying  glass  (mendacio  vitri),  that  their 
detection  was  most  difficult."  Coming  down  to  our  own 
times,  the  manufacture  of  false  jewellery  has  become  a 
thriving  industry,  that  both  employs  many  and  pleases 
many,  and  sometimes,  it  is  most  regrettable  to  say,  deceives 
many.  However,  in  these  days  of  enlightenment,  very 

F  2 


68  PRECIOUS   STONES. 

little  unscrupulous  work  is  done  in  passing  off  imitations  as 
genuine,  such  imitations  being  usually  sold  for  what  they 
are  worth,  and  nothing  more. 

One  of  the  most  celebrated  producers  of  imitations  of 
engraved  gems— in  modern  times — James  Tassie,  a  native 
of  Pollokshaws,  near  Glasgow,  settled  in  London  towards 
the  end  of  the  eighteenth  century,  and  there  copied  no 
less  than  1,500  rare  engraved  gems.  He  not  only  made 
copies,  but  also  original  cameo  portraits  of  his  contempo- 
raries, some  of  the  best  examples  of  this  class  of  work  that 
we  have. 

The  method  of  making  "  paste  "  copies  is  comparatively 
simple.  If  the  gem  to  be  copied  is  a  cameo,  a  mould  of 
the  raised  portion  is  first  taken  in  rotten  stone  or  other  fine 
coherent  powder ;  a  piece  of  glass  is  then  put  into  the 
mould  and  melted.  After  cooling  slowly,  the  cast  in 
glass  has  simply  to  be  trimmed,  the  back  ground  per- 
fectly flat,  and  cemented  on  to  a  suitable  background  of 
real  stone.  The  process  is  slightly  different  for  copying 
intaglios,  these  gems  having  the  subject  cut  or  sunk 
into  the  stone ;  therefore,  to  produce  a  copy,  an  impres- 
sion has  to  be  taken  first.  Imitation  intaglios  or  seals 
are,  however,  rare. 

The  glass,  or,  as  it  is  technically  known,  "  strass "  or 
"  paste"  (Italian,  past  a,  dough)  used  in  the  above  work  is, 
generally  speaking,  some  opaque  form,  maybe  translucent, 
rarely  transparent.  The  white  opaque  paste  is  made  by 
adding  oxide  of  tin  or  bone-ash  (phosphate  of  lime)  to  the 
ordinary  clear  glass  used  for  this  class  of  work.  These 
opaque  slags  being  much  like  Onyx,  Agate,  and  other 
varieties  of  the  so-called  "  Scotch  Pebble,"  great  quantities 


PEECIOUS  STONES.  69 

of  them  are  sold  as  such  mounted  in  brooches  and  different 
forms  of  jewellery. 

The  artist  may  have  used  Vesuvian  lava,  or  perhaps 
mother-of-pearl  shell  to  work  upon,  and  there  are  many 
such  cameos  to  be  had.  These  lava  gems,  if  gems  they  may 
be  called,  range  from  a  dirty  cream  colour  to  grey,  and 
almost  black.  They  are  easily  distinguishable  by  their 
colour,  opacity,  and  softness.  Of  course,  neither  of  these 
types  are  imitations,  but,  on  the  contrary,  may  be  genuine 
works  of  art,  though  not  necessarily  of  any  great  value. 
Many  fine  examples  of  cameo  exist  that  have  been  carved 
out  of  such  a  mineral  as  Steatite,  a  variety  of  Talc,  greenish 
or  grey  in  colour,  soft  and  very  soapy  to  the  touch,  in  fact, 
the  "  soap-stone  "  of  tailors. 

The  Assyrians,  Egyptians,  and  Greeks  used  Steatite, 
besides  harder  and  less  perishable  stones,  such  as  the. Onyx 
and  Carnelian.  Steatite  specimens  are  much  softer  than 
the  lava  forms. 

Paste  imitations  of  cameos  may  be  detected  by  placing 
them  in  hot  water.  This  dissolves  the  cement,  and  the 
front  separates  from  the  back.  Intaglios  are  more  difficult 
to  detect,  owing  to  the  object  being  in  one  piece. 

For  all  glass  imitations  of  semi-precious  or  precious 
stones,  the  test  of  hardness  is,  perhaps,  the  best,  for  the 
hardest  glass  used  in  their  production  can  be  easily  scratched 
by  an  ordinary  piece  of  flint,  whereas  the  glass  will  make 
no  impression  upon  the  flint.  The  specific  gravity  is  in 
nearly  all  cases,  with  the  exception  of  the  Sapphire, 
considerably  higher  than  that  of  the  stone  imitated.  Optical 
properties,  such  as  "  dichroism,"  or  unequal  absorption 
o£  certain  light  rays,  also  afford  good  tests,  glass  not 


70  PRECIOUS  STONES. 

being  dichroic.  Under  the  microscope  imitations  are 
seen  to  be  full  of  lines  and  striae,  signs  of  unequal  density 
and  strain.  There  are  also  innumerable  rounded  cavities 
or  bubbles  present,  unlike  the  angular  rents  and  vesicles  in 
natural  stones.  An  aluminium  pencil  drawn  across  the 
face  of  a  real  stone,  such  as  the  Diamond,  Sapphire,  Euby  or 
Emerald,  will  not  leave  any  mark  or  "  streak,"  but  if  drawn 
across  a  glass  surface  will  do  so.  This  test  is  only  applicable 
to  the  above  precious  stones. 

Before  dealing  with  the  production  of  imitation  and 
artificial  precious  stones,  for  convenience,  another  distinc- 
tion in  terms  may  be  made,  a  distinction  between  the  words 
"  imitation  "  and  "  artificial."  To  many  this  may  appear 
unnecessary,  the  two  terms  being  synonymous,  but  with 
the  advance  of  scientific  research  the  chemist  can  now 
make  in  the  laboratory  not  "  glass  imitations,"  but  "real 
stones  artificially,"  and  identical  in  composition  with  those 
found  in  Nature.  Their  artificial  production  is  quite 
modern,  carrying  us  back  only  a  generation  or  two,  but 
imitation  precious  stones  were  known  in  the  middle  ages,  if 
not  earlier.  They  were  certainly  known  to  the  alchemists,  for 
Saint  Thomas  Aquinas  mentions  imitation  Jacinth,  Sapphire, 
Emerald,  Topaz,  and  Euby.  In  the  middle  of  the  seven- 
teenth century  pastes  were  not  manufactured  according  to 
a  different  formula  for  each  stone,  as  had  formerly  been  the 
case,  but  to  one  general  formula,  much  the  same  as  that 
in  use  at  the  present  day. 

One  of  the  chief  difficulties  in  making  a  suitable  glass  is 
to  combine  hardness  with  a  high  index  of  refraction  and 
dispersive  power,  for  a  glass  having  the  latter  properties 
lacks  the  former,  and  "vice  versa."  The  dispersion  of 


PEECIOUS  STONES.  71 

thallium  glass  is  about  0*050,  and  of  the  Diamond  0*057,  so 

that  as  regards  the  greatest  charm  of  the  Diamond its 

dispersion  of  light — thallium  glass  is  almost  its  equal.  This 
is  why  imitation  diamonds  of  good  quality  look  so  well 
at  night.  But  what  this  glass  has  in  dispersive  powers  it 
lacks  in  hardness;  the  facets  lose  their  lustre,  become 
scratched,  and  owing  to  chemical  alteration,  it  goes  "  off 
colour "  and  takes  on  an  opacity  that  renders  it  in  time 
absolutely  worthless.  Glass  made  specially  for  imitation 
diamonds  must  have  a  high  index  of  refraction  and  disper- 
sive power,  even  though  it  lack  hardness ;  and  to  obtain 
such  a  glass  a  considerable  amount  of  lead  is  used  in  its 
manufacture.  Increase  of  lead  means  increase  of  dispersive 
power  but  decrease  in  hardness.  So  far  as  is  known,  lead 
seems  to  be  the  only  suitable  element  that  will  impart 
brilliancy  to  glass.  This  property  was  known  to  the  Romans ; 
but  after  the  fall  of  Rome,  it  seems  to  have  been  lost  and 
not  re-discovered  until  about  the  seventeenth  century, 
when  it  again  came  into  use  in  England,  and  English  glass 
was  considered  the  finest.  The  art  of  glass-making  for  all 
decorative  purposes  had  reached  a  very  high  standard  of 
perfection  in  ancient  Rome,  so  high,  in  fact,  that  it  is 
doubtful  if  we  equal  it  to-day  with  all  our  modern  methods 
and  improvements. 

M.  Feil,  of  Paris,  was  one  of  the  first  men  to  produce  a 
good  quality  strass,  and  as  a  result  imitations  are  now 
made  so  well  that  their  detection  is  exceedingly  difficult 
without  applying  suitable  scientific  tests. 

The  darkening  or  opacity  taken  on  by  paste  with  age  is 
due  to  the  sulphiding  of  the  lead.  This  sulphiding  is 
accelerated  in  large  towns  and  cities  where  there  is  an 


72  PKECIOUS   STONES. 

abundance  of  sulphurous  acid  in  the  air.  It  is  also  hastened 
very  considerably  by  the  amount  of  lead  present ;  some 
pastes  containing  over  50  per  cent.  The  following  per- 
centage composition  of  a  colourless  sample  will  give  some 
idea  of  the  constituents  : — 

Powdered  silica  or  Quartz     32  per  cent. 

Eed  oxide  of  lead    .         .     50       „ 

Potassium  carbonate       .     17       „        { ^Jj^Jj bj 

Borax  or  boron  trioxide         1       „ 

Alumina       .         .         .  trace 

Arsenious  oxide    .         .  trace  (sometimes). 

There  are  many  formulae,  all  much  the  same,  varying 
only  in  the  proportions  used  of  the  above  ingredients. 
Great  care  has  to  be  taken  in  the  fusion  to  prevent  froth- 
ing ;  the  mixture  is  fired  for  some  time  at  such  a  temperature 
that  caking,  or  as  it  is  technically  called,  "  fritting,"  only 
takes  place,  after  which  the  temperature  is  raised  until 
fusion  is  complete.  The  contents  of  the  crucible  are  then 
slowly  cooled,  precautions  being  taken  to  prevent  vibration 
or  any  disturbance  in  the  mass  likely  to  introduce  air 
bubbles ;  for  this  reason  the  glass  is  kept  molten  for  some 
time  after  complete  fusion.  This  clear  glass  is  used  for 
imitation  diamonds. 

Coloured  stones,  such  as  Kubies,  Amethysts,  etc.,  are 
imitated  by  adding  to  the  above  glass  traces  of  metallic 
oxides  or  other  suitable  colouring  mediums. 

The  imitation  ruby  is  made  by  fusing  together — 
1,000  parts  glass. 

40      ,,      oxide  of  antimony. 


PEECIOUS   STONES.  73 

1   part    purple  of  cassius  (compound  of  tin  and 

gold  chloride). 
1      „       gold. 

For  imitation  topaz  the  above  formula  is  used  minus  the 
gold,  and  the  fusion  is  not  carried  out  at  such  a  high  tem- 
perature. In  using  gold  for  colouring  purposes,  the 
greatest  care  has  to  be  taken  to  avoid  clouding  due  to 
reduction  of  the  gold  to  the  metallic  state.  The  colour 
taken  on  at  first  is  yellowish-green,  or  maybe,  brown,  a  deep 
ruby-red  being  obtained  on  annealing. 
Imitation  sapphire  .  1,000  parts  of  glass 

25       ,,       oxide  of  cobalt. 
,,        emerald    .  1,000       ,,       glass, 

8       ,,       copper  oxide 
0*2    „       chromium  oxide. 
,,        amethyst  .  1,000       „       glass, 

25       ,,       oxide  of  cobalt 
trace  oxide  of  manganese. 

,,        garnet       .  1,000       „       glass, 

trace  of  purple  of  cassius. 

,,        turquoise .  1,000       ,,       opaque  white  glass. 

trace  of  copper  oxide  or  oxide  of 

cobalt. 

Although  not  much  used  for  colouring  imitation  precious 
stones,  there  are  many  other  methods.  Various  shades  of 
yellow  may  be  obtained  by  the  addition  of  finely-powdered 
coal  to  glass  free  from  lead,  and  uranium  glass  is  coloured 
by  the  use  of  uranium  salts. 

Paste  has  to  be  cut  and  polished  in  the  same  manner  as 
real  stones,  only,  owing  to  the  inferior  hardness,  the  process 
is  much  more  simple.  Nearly  all  pastes  are  cut  as  brilliants, 


74  PEEOIOUS  STONES. 

this  method  setting  the  stone  off  to  best  advantage.  It 
needs  a  fairly  big  stone  to  work  upon,  as  the  brilliant  is 
almost  as  thick  as  it  is  broad.  Keal  Diamonds  that  are  not 
large  enough  or  contain  too  many  flaws  to  permit  cutting  in 
this  way  are  "rose"  or  "table"  cut;  but  such  a  method 
adopted  for  paste  would  be  useless.  Paste  absorbs  a  con- 
siderable amount  of  light,  especially  through  the  "  table." 
But  this  is  not  so  with  the  Diamond;  almost  the  whole  of 
the  light  falling  upon  it  is  entirely  reflected  off  again,  that 
which  is  absorbed  being  thrown  out  by  the  lower  facets. 
It  is  to  this  property  of  strong  refractivity  and  reflection 
that  the  Diamond  owes  its  brilliant  play  of  colours,  and 
experts  can  tell  real  stones  at  a  glance,  by  their  "  fire."  If 
an  imitation  diamond  cut  in  any  form  be  placed  in  a  good 
light  and  turned  about  in  various  directions  the  table  will* 
in  certain  positions  appear  as  a  black  spot  surrounded 
by  a  white  circle  of  light.  The  white  circle  of  light  is 
due  to  reflection  from  the  small  facets  between  the  table 
and  girdle,  and  the  blackness  of  the  table  itself  is 
largely  due  to  a  great  portion  of  the  light  falling  upon 
it  being  absorbed  and  not  thrown  out  again  by  the  lower 
facets. 

Imitations  when  examined  with  a  lens  are  frequently 
found  to  be  highly  fractured  round  the  girdle  where  clasped 
by  the  setting ;  the  fractures  being  conchoidal  or  shell-like 
and  characteristic  of  glass.  Keal  stones  rarely  show  this, 
at  least  not  round  the  girdle,  but  Diamonds  are  extremely 
liable  to  flaws,  and  I  strongly  recommend  that  purchasers 
of  stones  smaller  than  -J  of  an  inch  in  diameter,  or  less  than 
one  carat  in  weight,  should  examine  them  carefully  with  a 
powerful  lens.  One  stone  purchased  by  me  some  time  ago 


PEECIOUS   STONES.  75 

had  no  less  than  four  splits  in  the  base  or  "  collet,"  and 
one  small  one  half-way  across  the  "  table."  These 
flaws  Detracted  but  little  from  the  stone's  appearance  at 
night,  but  on  comparing  the  stone  with  a  perfect  one,  their 
effect  was  only  too  apparent. 

First-class  imitations  command  a  good  price,  owing  to 
the  cost  of  their  production ;  the  materials,  time  and  skill 
required  for  making  the  rough  glass  alone,  without  taking 
into  consideration  the  expense  of  cutting  and  polishing,  all 
tend  to  keep  really  fine  examples  of  this  class  of  work  from 
becoming  cheap.  Very  cheap  forms  of  paste  are  to  be 
purchased,  but  they  will  not  stand  comparison  with  better 
qualities. 

Although,  strictly  speaking,  pearls  do  not  belong  to  the 
mineral  kingdom,  it  may  not  be  out  of  place  in  an  article  of 
this  nature  to  mention  briefly  the  method  of  making 
imitations.  They  are  so  perfectly  made,  besides  being  not 
quite  so  perishable  or  liable  to  decay  as  real  pearls,  that  the 
latter  as  a  consequence  have  fallen  very  considerably  in 
value.  They  were  first  imitated  by  Jacquin  at  Paris  in  1656, 
and  the  method  in  vogue  to-day  is  much  the  same  as  that 
he  discovered.  It  consists  in  blowing  small  spheres  of 
opalescent  glass  coated  internally  with  a  preparation  known 
as  "Essence  d'Orient,"  made  from  the  scales  of  such  a  fish 
as  the  Bleak.  The  sphere  is  slightly  dented,  coated 
externally  and  internally  with  parchment  size  and  pearl 
essence,  and  then  filled  in  with  wax.  Pearls  imitated  in 
this  way  are  exceedingly  beautiful,  and  have  a  rich  and 
charming  lustre.  They  may  be  known  by  their  hardness, 
which  is  very  much  greater  than  that  of  real  pearls,  and  by 
their  extreme  brittleness,  the  slightest  pressure  causing 


76  PBECIOUS   STONES. 

them  to  crack.  Again,  their  lustre  may  be  described  as 
vitreous  or  glassy,  whereas  in  genuine  pearls  the  lustre  is 
soft,  indeed  almost  dull. 

Coming  now  to  the  question  of  real  stones,  some  methods 
of  "  faking  "  them,  by  altering  or  improving  their  colour, 
might  with  advantage  be  briefly  touched  upon  before 
proceeding  to  the  more  interesting  subject  of  making  them 
artificially. 

The  colour  of  some  stones  may  be  altered  by  heat,  and 
the  process  of  "  burning  "  is  one  that  was  in  use  by  the 
ancient  Egyptians.  Pliny  also  refers  to  it  in  his  time,  and 
the  method  practised  then  is  the  same  as  that  in  use  to-day. 
It  consists  in  either  wrapping  the  stone  up  in  tinder  and 
setting  fire  to  the  tinder,  or  packing  the  stone  in  very  fine 
powder,  such  as  rotten  stone  or  earth,  and  baking  in  a  clay 
crucible.  Precautions  have  to  be  taken  not  to  heat  too 
highly,  or  the  stone  may  be  hopelessly  fissured.  The  yellow 
Brazilian  Topaz  assumes  a  beautiful  rose-red  colour,  and  is 
then  known  as  Burnt  Topaz.  The  colour  is  discharged  from 
blue  Sapphires  by  burning,  and  they  become  clear.  Eubies 
are  quite  unaffected,  and  retain  their  original  colour. 
Carnelians  may  be  intensified  in  colour  and  much  improved. 
Stones  are  coloured  also  by  soaking  in  chemical  solutions. 
There  are  many  different  methods.  Perhaps  the  principal 
one  in  use  is  that  for  the  production  of  black-and-white 
Onyx.  An  ordinary  Onyx  consists  of  alternate  layers  of  blue 
Chalcedony  (a  crypto-crystalline  form  of  silica)  and  white 
opaque  Cachalong,  another  variety  of  silica.  The  Chalce- 
dony layers  are  slightly  porous,  and  if  soaked  in  oil  for  some 
time  absorb  a  certain  amount ;  this  is  blackened  by 
de-hydrating  with  strong  sulphuric  acid.  Small  specimens 


PBECIOUS  STONES.  77 

may  be  done  in  half  an  hour  by  carefully  boiling  in  pure 
olive  oil  and  then,  after  drying,  putting  them  into  the  acid. 
If  they  become  too  black,  their  original  colour  may  be 
restored,  or,  in  other  words,  the  blackness  may  be  removed 
by  warming  in  pure  nitric  acid.  A  solution  of  sugar  may 
be  substituted  for  oil. 

"Off-colour"  or  yellowDiamonds, known  as  "straws,"  have 
been  passed  off  by  unscrupulous  dealers  as  "  first  water  " 
stones  by  dyeing  them  with  a  magenta  varnish,  which 
neutralises  the  colour.  This  in  time  wears  off  and  their 
true  colour  shows  up.  Soaking  a  suspected  stone  in  abso- 
lute alcohol  for  a  moment,  and  wiping,  will  soon  remove  any 
varnish  if  there  be  any  to  remove. 

A  method  of  fraud  very  little  practised,  perhaps,  because 
it  entails  no  little  skill  and  the  use  of  real  stones,  is  the 
production  of  "  doublets  "  and  "  triplets." 

A  Diamond  or  Sapphire,  more  often  the  latter,  that, 
owing  to  shape  or  the  number  of  flaws  it  contained,  would 
be  useless  for  cutting  as  a  brilliant,  is  cut  as  half  a  one,  i.e., 
the  upper  or  table  portion.  This  portion  is  then  ground 
perfectly  flat  at  the  back  and  cemented  by  means  of  a  clear 
transparent  cement  to  the  lower  or  collet  half,  cut  from 
either  Sapphire  or  paste  as  the  case  may  be.  Such  a  stone 
when  clasped  is  difficult  to  detect,  but  on  being  removed 
from  the  setting  and  placed  in  warm  water,  the  cement  is 
dissolved,  and  the  two  portions  fall  apart  much  the  same 
as  when  dealing  with  imitation  cameos. 

Coloured  stones  imitated  by  the  above  process  have  a  thin 
slice  of  real  stone  set  between  the  two  halves,  or  the  cement 
used  may  be  coloured.  It  is  to  specimens  set  up  in  the 
former  method  that  the  term  "triplet"  is  applied. 


78  PBECIOUS  STONES. 

Coming  now  to  the  subject  of  making  real  stones 
artificially,  it  is  one  of  great  interest,  not  only  to  scientists 
and  dealers  in  precious  stones,  but  to  the  jewel-loving 
public.  It  is  a  subject  almost  as  fascinating  and  interesting 
to  the  experimental  chemist  of  to-day  as  the  search  for  the 
mythical  "philosopher's  stone"  was  in  the  days  of  the 
early  alchemists.  Commercially  speaking,  it  is  a  remark- 
able fact  that  in  these  days  of  progressive  scientific 
research  very  little  headway  has  been  made  in  the  synthesis 
of  real  stones  of  saleable  quality.  Certainly,  the  Diamond, 
one  of  the  most  difficult  to  produce,  has  been  artificially 
prepared  in  the  laboratory.  The  experiments  and  their 
results  from  a  scientific  point  of  view  are  interesting,  but 
at  a  great  outlay  for  such  results,  the  time  and  money 
expended  being  considerable.  The  stones,  after  laborious 
and  tedious  extraction  from  the  matrix  in  which  they 
were  formed,  could  only  be  well  seen  with  a  lens ;  they  were 
hardly  fit  to  grace  the  movement  of  a  watch,  far  less  adorn 
a  lady's  finger. 

Many  of  the  most  talented  chemists  of  the  world  have 
given  the  matter  their  consideration,  and  the  production  of 
a  large  number  of  minerals  and  rocks  with  a  few  of  the  so- 
called  precious  stones  is  now  an  accomplished  fact,  although, 
as  already  stated,  not  a  commercial  success.  Our  present 
knowledge  of  the  subject  has  grown  considerably  by  the 
investigations  of  such  men  as  Gustav  Eose,  Mitscherlich, 
Credner,  Deville,  Debray,  Kuplmann,  Heintz,  Manross, 
Daubree,  Senarmont,  Hautefeuille,  Berthier,  Forchammer, 
Wohler,  Becquerel,  Wibel,  Moissan,  Ebelman,  Fraube, 
Crookes,  Noble,  Fouque,  Sorby  and  Levy,  and  many  other 
noted  experimentalists. 


PEECIOUS  STONES.  79 

One  of  the  chief  difficulties  to  overcome  in  the  synthetical 
preparation  of  a  mineral  is  crystallisation.  Nearly  all 
minerals  crystallise  in  some  form,  and  more  particularly 
is  this  so  with  precious  stones,  excepting  the  Opal  and 
Turquoise.  Now  Nature  has  one  great  advantage  over  our 
puny  experiments  in  the  laboratory  :  she  can  take  unlimited 
time  and  has  great  stores  of  energy  at  her  command,  enor- 
mous pressures  and  high  temperatures  working  together 
or  independently.  In  the  laboratory,  on  the  other  hand, 
pressure  and  temperature,  although  obtainable,  are  in  many 
cases  not  sufficiently  high,  and  also  not  easily  controlled. 
Then,  again,  as  regards  time,  poor  man  does  not  live  long 
enough.  Working  under  conditions  such  as  these  Nature 
need  have  little  fear  of  being  ousted  from  the  Diamond 
market.  Whatever  method  we  may  adopt  in  our  experi- 
ments, time  will  not  wait,  and  crystals  of  fair  size  and 
shape  are  not  made  in  five  minutes,  so  the  result  is, 
generally  speaking,  a  few  microscopic  splinters  hardly 
worth  looking  at.  If  sufficient  time  could  be  given  in 
many  of  the  experiments  carried  out,  for  crystallisation 
to  take  place  slowly,  then  one  of  the  chief  difficulties 
would  be  overcome. 

Even  presuming  we  knew  definitely  how  some  precious 
stones  were  formed  in  Nature's  laboratory,  it  is  doubtful 
whether  we  could  apply  Nature's  methods  in  our  laboratories 
to  produce  similar  results.  Many  have  been  the  theories 
put  forward  to  explain  the  origin  of  that  monarch  of 
precious  stones — the  Diamond,  one  in  some  cases  being  as 
feasible  as  another  ;  but  at  the  present  day  it  is  difficult  to 
apply  any  one  of  them  as  correct.  To  chemists  and 
physicists,  from  early  times,  this  stone  has  been  the  subject 


80  PRECIOUS   STONES. 

of  discussion.  What  does  the  Diamond  consist  of  ?  How 
was  it  formed  ?  Can  it  be  made  artificially  ?  Thanks  to 
the  rapid  progress  in  scientific  research,  all  these  questions 
have  been  answered,  perhaps  not  quite  so  successfully  as  we 
desire,  but  still  in  a  satisfactory  manner. 

The  composition  of  the  Diamond  was  early  observed  by 
Gassiot  and  Berzelius  ;  and  Lavosier,  in  1772,  showed  that  if 
heated  to  a  high  enough  temperature  (about  800°  C.  accord- 
ing to  Moissan)  it  burned  away,  producing  by  combination 
with  the  oxygen  of  the  air  that  heavy  noxious  gas,  carbon 
anhydride  (carbonic  acid),  the  after-damp  or  choke-damp  of 
coal  pit  explosions.  Smithson  Tennant,  in  1779,  proved 
that  carbonic  acid  was  the  only  product  of  the  Diamond's 
combustion.  This  was  verified  by  Davy  in  1814,  who  was 
the  first  to  prove  that  it  consisted  almost  wholly  of  pure 
carbon,  the  residue  after  combustion  being  only  0'2  to 
0*05  per  cent,  of  an  ash  made  up  of  silica  and  oxide  of 
iron.  One  of  the  earliest  theories  of  the  Diamond's 
origin  was  propounded  by  Sir  Isaac  Newton,  who  stated 
that  it  is  in  all  probability  "  an  unctuous  substance 
coagulated."  This  theory,  no  doubt,  was  based  upon  its 
high  refractive  properties,  ordinary  gum  arabic  being  not 
at  all  unlike  rough  Diamonds.  A  similar  theory  put 
forward  by  Sir  David  Brewster  was  that  it  owed  its  origin 
to  the  vital  processes  of  plants,  and  was  at  one  time 
viscous,  like  resin. 

For  a  considerable  time  theory  held  first  place  and 
practical  experiments  gave  no  satisfactory  results.  Theory 
after  theory  followed  each  other  in  rapid  succession  from 
such  men  as  D'Orbigny,  Wohler,  Liebig,  Berthelot,  Bischof, 
C.  0.  Von  Leonhard,  Parrot,  Carvill  Lewis,  Wilson,  Goppert 


PBECIOUS  STONES.  81 

and  Dana,  many  agreeing  and  many  disagreeing.  Damour 
and  Gannal,  of  Brazil,  considered  that  the  Diamond  might 
be  due  to  the  reduction  of  carbon  bi- sulphide  (an  evil  smell- 
ing impurity  of  coal  gas).  A.  Favre,  and  later  the  Hon. 
St.  Claire  Deville,  were  led  by  a  study  of  the  minerals 
associated  with  the  Diamonds  of  Brazil  to  consider  their 
formation  the  result  of  the  reduction  of  fluorine  or  chlorine 
compounds  of  carbon.  Whether  this  may  be  the  true 
origin  of  Brazilian  Diamonds  or  not,  it  is  the  writer's 
opinion  that  if  successful  experiments  are  undertaken  in 
the  laboratory  it  will  be  in  the  reduction  of  such  carbon 
compounds. 

Perhaps  one  of  the  first  experiments  on  the  artificial 
production  of  Diamonds  to  meet  with  any  success  was 
carried  out  by  Despritz  in  1853.  The  method  employed  by 
him  was  to  pass  the  electric  spark  in  vacuo  for  a  month, 
using  a  platinum  rod  as  one  terminal  and  a  carbon  cylinder 
as  the  other.  The  platinum  terminal  was  found  to  be 
encrusted  with  minute  octahedral  crystals  which  answered 
all  the  tests  applicable  to  the  Diamond. 

In  1880  J.  B.  Hannay,1  of  Glasgow,  carried  out  no  less  than 
eighty  experiments  upon  the  reduction  of  a  carbon  com- 
pound, only  three  of  which  were  successful.  Iron  tubes 
20  inches  long  by  1  inch  thick  and  \  inch  bore  were 
filled  about  two-thirds  full  of  pure  paraffin  spirit  with 
a  little  charcoal,  and  then  sealed  off.  The  sealing  of  these 
tubes  was  the  most  difficult  part  of  the  undertaking.  In  the 
earlier  experiments  screw  stoppers,  luted  in  with  a  mixture 
of  silicate  of  soda  and  manganese  dioxide,  were  used,  but 

1  "  Artificial  Production  of  Diamonds,"  by  J.  B.  Hannay,  F.E.S.E., 
Proc.  Eoy.  Soc.,  No.  204,  1880. 

P.S,  G 


82  PEEOIOUS  STONES. 

after  heating  for  four  hours  in  a  reverberatory  furnace,  the 
tubes  on  opening  were  found  to  be  empty,  owing  to  leakage. 
Later,  he  tried  plugging  with  iron  balls,  the  upper  end  of 
the  tube  being  narrowed  after  the  introduction  of  the  ball, 
which  was  then  drawn  up  and  luted.  This  method  was 
worse  than  the  former,  not  as  regards  leakage,  but  damage, 
as  they  either  burst  with  considerable  violence  or  the  balls 
were  blown  out.  After  this,  welding  was  resorted  to.  Now 
it  is  obvious  that,  when  three  parts  full  of  spirit,  this  pro- 
ceeding required  considerable  skill,  the  ends  of  the  tubes 
having  to  be  immersed  in  a  freezing  mixture.  There  were 
many  failures  due  to  bursting,  whilst  firing,  or  very  often  a 
tube  would  burst  with  a  loud  explosion  when  being  opened. 
This  latter  operation  was  in  almost  every  case  very  difficult, 
owing  to  the  hardening  of  the  inner  part  of  the  tube  by 
conversion  of  the  iron  into  steel.  The  mixture  used  by 
Mr.  Hannay  in  his  three  successful  experiments  was  4 
grams  of  lithium  in  a  solution  of  bone  oil  90  per  cent,  and 
paraffin  10  per  cent.,  the  tube  being  three  parts  full,  welded 
off  and  brought  to  a  red  heat  in  an  inclined  reverberatory 
furnace  for  fourteen  hours.  The  hard  crystalline  cake 
obtained  yielded  minute  Diamonds  having  all  the  properties 
of  real  stones  and  consisting  of  97' 85  per  cent,  pure  carbon 
with  a  trace  of  nitrogen. 

Since  1893  various  experiments  have  been  carried  out, 
and  with  the  advance  in  electricity  a  great  power  has 
been  placed  in  the  hands  of  the  experimentalist.  The 
late  H.  Moissan,  of  Paris,  obtained  very  successful  results 
with  the  electric  furnace,  and  produced  many  different 
minerals,  including  Diamonds  over  0'5  m.m.  in  size.  It 
would  be  of  interest  as  showing  the  time  and  skill  required 


PRECIOUS  STONES.  83 

to  make  a  few  small  splinters  of  Diamond  to  here 
give  Moissan's  method  from  Sir  W.  Crookes'  paper  on 
"  Diamonds,"  l  by  that  author's  kind  permission  : — 

"  For  the  manufacture  of — I  am  afraid  I  must  say  an 
infinitesimal — diamond,  the  first  necessity  is  to  select  pure 
iron — free  from  sulphur,  silicon,  phosphorus,  etc., — and  to 
pack  it  in  a  carbon  crucible  with  pure  charcoal  from  sugar. 
The  crucible  is  then  put  into  the  body  of  the  electric  fur- 
nace, and  a  powerful  arc  formed  close  above  it  between 
carbon  poles,  utilising  a  current  of  700  amperes  at  40  volts 
pressure.  The  iron  rapidly  melts  and  saturates  itself  with 
carbon.  After  a  few  minutes'  heating  to  a  temperature 
above  4,000°  C.-  a  temperature  at  which  the  iron  melts 
like  wax  and  volatilises  in  clouds — the  current  is  stopped, 
and  the  dazzling  fiery  crucible  is  plunged  beneath  the  sur- 
face of  cold  water,  where  it  is  held  till  it  sinks  below  a  red 
heat.  As  is  well  known,  iron  increases  in  volume  at  the 
moment  of  passing  from  the  liquid  to  the  solid  state.  The 
sudden  cooling  solidifies  the  outer  layer  of  iron  and  holds 
the  inner  molten  mass  in  a  tight  grip.  The  expansion  of 
the  inner  liquid  on  solidifying  produces  an  enormous  pres- 
sure, and  under  the  stress  of  this  pressure  the  dissolved 
carbon  separates  out  in  transparent  forms — minutely 
microscopic,  it  is  true — all  the  same  veritable  diamonds, 
with  crystalline  form  and  appearance,  colour,  hardness, 
and  action  on  light  the  same  as  the  natural  gem. 

"  Now  commences  the  tedious  part  of  the  process.     The 

1  "Diamonds."  A  lecture  delivered  before  the  British  Association 
at  Kimberley,  September  15,  1905,  by  Sir  William  Crookes.  Published 
at  the  Chemical  News  Office,  16,  Newcastle  Street,  Farringdon  Street, 
London.  Price  Is. 

G   2 


84  PBECIOUS   STONES. 

metallic  ingot  is  attacked  with  hot  nitro-hydrochloric  acid 
until  no  more  iron  is  dissolved.  The  bulky  residue  con- 
sists chiefly  of  graphite,  together  with  translucent  chestnut- 
coloured  flakes  of  carbon,  black  opaque  carbon  of  a  density 
of  from  3*0  to  3*5,  and  hard  as  diamonds — black  diamonds 
or  carbonado,  in  fact — and  a  small  portion  of  transparent 
colourless  diamonds  showing  crystalline  structure.  Besides 
these,  there  may  be  carbide  of  silicon  and  corundum,  arising 
from  impurities  in  the  materials  employed. 

"  The  residue  is  first  heated  for  some  hours  with  strong 
sulphuric  acid  at  the  boiling  point,  with  the  cautious  addi- 
tion of  powdered  nitre.  It  is  then  well  washed  and  for  two 
days  allowed  to  soak  in  strong  hydrofluoric  acid  in  cold, 
then  in  boiling  acid.  After  this  treatment  the  soft  graphite 
disappears,  and  most,  if  not  all,  the  silicon  compounds  have 
been  destroyed.  Hot  sulphuric  acid  is  again  applied  to 
destroy  the  fluorides,  and  the  residue,  well  washed,  is 
attacked  with  a  mixture  of  the  strongest  nitric  acid  and 
powdered  potassium  chlorate,  kept  warm — but  not  above 
60°  C.,  to  avoid  explosions.  This  treatment  must  be  repeated 
six  or  eight  times,  when  all  the  hard  graphite  will  gradually 
be  dissolved,  and  little  else  left  but  graphitic  oxide, 
diamond,  and  the  harder  carbonado  and  boart.  The  residue 
is  fused  for  an  hour  in  fluorhydrate  of  fluoride  of  potassium, 
then  boiled  out  in  water,  and  again  heated  in  sulphuric 
acid.  The  well-washed  grains  which  resist  this  energetic 
treatment  are  dried,  carefully  deposited  on  a  slide,  and 
examined  under  the  microscope.  Along  with  numerous 
pieces  of  black  diamond  are  seen  transparent  colour- 
less pieces,  some  amorphous,  others  with  a  crystalline 
appearance.  Although  many  fragments  of  crystals  occur, 


PRECIOUS  STONES.  85 

it  is  remarkable  I  have  never  seen  a  complete  crystal.  All 
appear  shattered,  as  if  on  being  liberated  from  the  intense 
pressure  under  which  they  were  formed  they  burst  asunder. 
I  have  singular  evidence  of  this  phenomenon.  A  fine  piece 
of  artificial  diamond,  carefully  mounted  by  me  on  a  micro- 
scopic slide,  exploded  during  the  night  and  covered  the 
slide  with  fragments.  Moissan's  crystals  of  artificial 
diamond  sometimes  broke  a  few  weeks  after  their  prepa- 
ration, and  some  of  the  diamonds  which  cracked  weeks  or 
even  months  after  their  preparation  showed  fissures  covered 
with  minute  cubes.  This  bursting  paroxysm  is  not  unknown 
at  the  Kimberley  mines. 

"  So  far,  these  specimens  are  all  microscopic.  The 
largest  artificial  diamond  is  less  than  1  m.m.  across. 
These  laboratory  diamonds  burn  in  the  air  before  the 
blowpipe  to  carbonic  acid.  In  lustre,  crystalline  form, 
optical  properties,  density,  and  hardness,  they  are  identical 
with  the  natural  stone. 

"  In  several  cases  Moissan  separated  ten  to  fifteen  micro- 
scopic diamonds  from  a  single  ingot.  The  larger  of  these 
are  about  0*75  m.m.  long  ;  the  octahedra  being  0'2  m.m." 

Again,  to  quote  from  Sir  William  Crookes'  paper  :— 

"  A  NEW  FORMATION  OF  DIAMOND. 

"  I  have  long  speculated  as  to  the  possibility  of  obtaining 
artificially  such  pressures  and  temperatures  as  would  fulfil 
the  above  conditions.  In  their  researches  on  the  gases  from 
fired  gunpowder  and  cordite,  Sir  Frederick  Abel  and  Sir 
Andrew  Noble  obtained  in  closed  steel  cylinders  pressures 
as  great  as  95  tons  to  the  square  inch,  and  tempera- 
tures as  high  as  4,000°  C.  According  to  a  paper  recently 


86  PRECIOUS  STONES. 

communicated  to  the  Koyal  Society,  Sir  Andrew  Noble, 
exploding  cordite  in  closed  vessels,  has  obtained  a  pressure 
of  8,000  atmospheres,  or  50  tons  per  square  inch,  with  a 
temperature  reaching  in  all  probability  5,400°  absolute. 

"  Here,  then,  we  have  conditions  favourable  for  the 
liquefaction  of  carbon,  and  were  the  time  of  explosion 
sufficient  to  allow  the  reactions  to  take  place,  we  should 
certainly  expect  to  get  the  liquid  carbon  to  solidify  in  the 
crystalline  state. 

"By  the  kindness  of  Sir  Andrew  Noble  I  have  been 
enabled  to  work  upon  some  of  the  residues  obtained  in 
closed  vessels  after  explosions,  and  I  have  submitted  them 
to  the  same  treatment  that  the  granulated  iron  had  gone 
through.  After  weeks  of  patient  toil  I  removed  the  amor- 
phous carbon,  the  graphite,  the  silica,  and  other  constituents 
of  the  ash  of  cordite,  and  obtained  a  residue  among  which, 
under  the  microscope,  crystalline  particles  could  be  dis- 
tinguished. Some  of  these  particles,  from  their  crystalline 
appearance  and  double  refraction,  were  silicon  carbide ; 
others  were  probably  diamonds.  The  whole  residue  was 
dried  and  fused  at  a  good  red  heat  in  an  excess  of  potassium 
bifluoride,  to  which  was  added  during  fusion  5  per  cent,  of 
nitre.  (Previous  experiments  had  shown  me  that  this 
mixture  readily  attacked  and  dissolved  silicon  carbide ;  un- 
fortunately it  also  attacks  diamond  to  a  slight  degree.)  The 
residue,  after  thorough  washing  and  then  heating  in  fuming 
sulphuric  acid,  was  washed,  dried,  and  the  largest  crystal- 
line particles  picked  out  and  mounted.  All  the  operations 
of  washing  and  acid  treatment  were  performed  in  a  large 
platinum  crucible  by  decantation  (except  the  preliminary 
attack  with  nitric  acid  and  potassium  chlorate,  when  a 


PRECIOUS  STONES.  87 

hard  glass  vessel  was  used) ;  the  final  result  was  washed 
into  a  shallow  watch-glass  and  the  selection  made  under 
the  microscope. 

"  From  the  treatment  they  have*  undergone,  chemists 
will  agree  with  me  that  diamonds  only  could  stand  such  an 
ordeal  ;  on  submitting  them  to  skilled  crystallographic 
authorities  my  opinion  is  confirmed." 

Another  method,  evidently  new,  is  put  forward  by  Mr. 
C.  Y.  Burton,  of  Cambridge.  This  gentleman,  writing  in 
Nature,1  states  that  lead  containing  about  1  per  cent, 
of  calcium  is  capable  of  holding  a  certain  amount  of  carbon 
in  solution  either  in  the  free  state  or  as  calcium  carbide. 
This  carbon  crystallises  out  in  the  form  of  minute  octahedral 
crystals,  having  all  the  properties  of  the  Diamond  if  the 
calcium  be  eliminated.  To  get  rid  of  the  calcium,  or  rather 
to  render  it  inert,  he  passes  steam  through  the  molten 
mass,  converting  it  by  this  means  into  calcium  hydrate. 
The  lead  is  unaffected,  and  at  a  dull  red  heat  the  carbon 
crystallises  out  as  above,  but  if  at  a  full  red  heat  only 
Graphite  is  obtained. 

Besides  the  above  experiment,  Mr.  Burton  has  been 
successful  in  the  reduction  of  carbon  compounds,  such  as 
benzene,  toluene,  carbon  tetrachloride,  etc.,  in  sealed  tubes 
and  bombs,  at  temperatures  of  200°  C.  and  300°  C. 

In  1898,  J.  Friedlander  produced  some  smoky  crystals 
having  all  the  properties  of  the  Diamond  by  fusing  the 
mineral  Olivine  (an  iron  silicate  of  magnesia)  in  a  gas  blow- 
pipe, the  fusion  being  stirred  frequently  with  a  stick  of  pure 
Graphite  ;  after  cooling  this  was  found  to  be  encrusted  with 
exceedingly  small  crystals  of  Diamond. 

1  "  Artificial  Diamonds,"  Nature,  p.  397,  Vol.  72,  August  24,  1905. 


88  PEECIOUS  STONES. 

It  is  obvious  from  the  foregoing  remarks  upon  various 
experiments  and  their  results  that  the  Diamond  market 
is  not  likely  to  be  threatened  in  the  near  future  by 
their  wholesale  and  retail  manufacture  in  the  chemical 
laboratory. 

Many  of  the  experiments,  however,  are  interesting 
from  another  point  of  view — they  throw  some  light 
upon  the  probable  origin  of  the  Diamond.  Moissans' 
experiments  help  to  explain  its  occurrence  in  meteoric 
iron,  or  perhaps  the  origin  of  the  South  African  stones. 
Sir  William  Crookes  considers  that  the  latter  have  been 
formed  in  some  such  manner,  the  matrix  in  the  "pipes" 
being  highly  ferruginous.  Friedlander's  experiment,  on  the 
other  hand,  seems  to  suggest  that  they  may  have  been  formed 
by  the  action  of  a  molten  silicate  upon  Graphite  or  other 
carbonaceous  matter.  It  is  possible  both  reactions  may 
have  taken  place  together,  but  it  is  hardly  within  the  scope 
of  the  present  chapter  to  consider  it,  and  the  writer  can 
only  refer  those  at  all  interested  to  Sir  William  Crookes' 
paper. 

Without  any  hesitation,  it  may  be  said  that  the  first 
precious  stone  to  be  successfully  prepared  in  the  laboratory 
was  that  most  beautiful  of  precious  stones — the  Euby — the 
only  stone  that  ranks  with,  and  can  even  rank  above,  the 
Diamond  in  value. 

St.  Claire  Deville  and  A.  Carron  in  1858,1  succeeded  in 
producing  crystals  of  Kuby,  Sapphire  and  Corundum  by 
fusing  at  a  high  temperature  a  mixture  of  boric  anhydride 
and  aluminium  fluoride  ;  the  boron  combining  with  the 
fluorine  volatilises  off,  and  the  aluminium  is  oxidised  into 
1  "  Comptes  Eendus,"  vol.  xlvi. 


PBECIOUS  STONES.  89 

alumina,  which  crystallises  out  as  one  of  the  above  three 
varieties  according  to  the  colouring  medium  added ;  this 
may  be  a  trace  of  potassium  dichromate  or  chromium 
fluoride,  the  colour  produced  depending  upon  the  amount 
used,  a  mere  trace  of  the  latter  giving  the  Kuby,  a  little 
more  the  Sapphire,  and  still  more  producing  green  Corundum. 

J.  Morozewiez  employed  somewhat  similar  methods,  and 
obtained  Spinels  (oxide  of  magnesium  and  aluminium)  and 
crystals  of  Corundum  1*5  m.m.  in  diameter,  the  colour, 
however,  not  being  due  to  chromium,  but  iron. 

For  good  Sapphire  blues  the  writer  has  found  a  trace  of 
cobaltic  nitrate  to  be  the  best. 

From  a  commercial  point  of  view,  the  most  successful 
experiments  ever  carried  out  were  by  Fremy  and  Verneuil 
in  1878,  and  later  in  1890,  when  they  produced  Eubies  of 
such  good  quality  and  size  that  they  were  sold  for  watch- 
makers' purposes.  They  fused  in  a  clay  crucible,  at  a 
temperature  of  about  1,500°  C.  a  mixture  of  alumina  and 
barium  fluoride  containing  a  trace  of  potassium  di-chromate. 
The  fusion  was  kept  molten  for  a  week,  and  then  cooled 
down  very  slowly,  small  crystals  of  Euby — and,  if  cobalt 
oxide  was  substituted  for  the  di-chromate — Sapphires 
separating  out  in  the  mass. 

In  1885  Eubies  were  put  on  the  market  of  sufficient  size 
and  quality  to  be  mounted,  cut  or  uncut,  for  jewellery. 
These  stones,  upon  examination  with  a  lens,  were  seen  to 
have  been  artificially  made,  as  they  contained  many  minute 
bubbles  and  other  signs  of  strain.  They  were  produced  in 
Geneva,  and  received  the  name  of  "  Geneva  Eubies,"  but 
the  method  of  their  production  was  a  trade  secret,  and,  as 
far  as  the  writer  is  aware,  is  still  so. 


90  PRECIOUS  STONES. 

In  a  paper  by  A.  Verneuil,  in  1904,  "  On  the  Artificial 
Eepr eduction  of  the  Kuby  by  Fusion,"1  he  describes  a  new 
method  devised  by  him  that  has  proved  highly  satisfac- 
tory, some  of  the  stones  prepared  weighing  up  to  15  carats 
and  measuring  over  5  m.m.  in  diameter.  The  smaller 
stones  are,  however,  the  best,  being  free  from  bubbles,  which 
are  unfortunately  always  present  in  the  larger  ones,  and  at 
once  indicate  their  origin. 

M.  Yerneuil  found  that  one  of  the  chief  difficulties  to 
overcome  was  cooling;  for  if  cooled  too  quickly  the  alumina 
becomes  slaggy  and  an  enamel  is  produced.  He  invented 
a  most  ingenious  piece  of  blow-pipe  apparatus,  by  means  of 
which  he  could  bring  about  the  gradual  fusing  and  as 
gradual  cooling.  The  blow-pipe  and  furnace-tube  were 
made  vertically,  and  very  finely  powdered  alumina  contain- 
ing a  trace  of  chromic  oxide  was  fed  into  the  tube  through 
a  sieve  by  means  of  a  series  of  regular  taps  controlled  by 
an  electro-magnet.  This  arrangement  causes  the  material 
to  fall  down  the  tube  intermittently  in  a  series  of  thin 
layers.  These  layers  gradually  grow  upwards  in  the  shape 
of  a  cone,  the  apex  of  which  fuses  on  reaching  a  hot  enough 
part  of  the  tube ;  the  fused  mass  then  extends  in  the  form 
of  a  long  filament.  This,  on  reaching  a  still  hotter  part  of 
the  furnace-tube  fuses  into  a  spherical  mass,  which  on 
cooling  slowly,  has  all  the  properties  of  the  natural  Euby. 

As  the  cost  of  producing  artificial  Eubies  is  very  high, 
they  are  quite  as  dear  as  the  natural  stones. 

Having  described  some  of  the  methods  of  making  Eubies, 

1  "  Memoire  sur  la  Eeproduction  Artificielle  du  Eubis  par  Fusion," 
By  A.  Verneuil  ("  Annales  de  Chemie  et  de  Physique,"  8e  sene  t.  ii., 
Sept.  1904). 


PEECIOUS  STONES.  91 

Sapphires,  and  Corundum,  we  might  briefly  consider  one  or 
two  experiments  carried  out  upon  the  preparation  of  Zircons, 
Emeralds  and  Turquois,  these  stones  being  the  only  others 
successfully  reproduced  in  the  laboratory. 

By  the  action  of  gaseous  silicon  fluoride  upon  zirconia 
(zirconium  oxide),  crystals  of  Zircon  (silicate  of  -zirconium) 
were  formed.  Experiments  of  this  nature  are  somewhat 
dangerous  to  do,  as  fluorine  compounds,  especially  if  gaseous, 
are  very  deadly,  and  will  attack  almost  anything.  The  acid 
used  for  etching  glass  if  it  comes  in  contact  with  the  skin 
produces  painful  sores.  Substituting  beryllium  oxide  for 
zirconia  in  the  above  experiment,  hexagonal  plates  similar 
in  hardness  to  the  Emerald  were  obtained.  None  of  these 
methods  are,  however,  of  commercial  importance. 

The  Turquoise,  owing  to  its  amorphous  nature  and  opacity, 
has,  besides  many  forms  of  imitation  and  substitutes,  such  as 
Malachite,  Bone  Turquoise  or  Odontolite,  etc.,  been  so  success- 
fully prepared  artificially  that  without  destroying  the  stone 
it  is  difficult  to  distinguish  between  the  natural  and  the 
laboratory  production.  They  are  as  a  rule  mixed  up  with 
parcels  of  natural  stones  in  the  rough,  and  are  in  many  cases 
much  finer  than  the  real  Turquoise.  To  make  their  appear- 
ance more  natural,  they  are  stained  with  Limonite  (hydrous 
oxide  of  iron),  and  their  detection  as  a  consequence  is  some- 
what difficult.  It  is  stated  by  Dr.  Max  Bauer,  in  his  admir- 
able book  on  "  Precious  Stones,"1  that  if  these  stones  are 
put  into  water  they  darken  in  colour,  and  minute  cracks  may 
be  seen  on  the  surface  if  examined  with  a  lens.  The  only 

1  "  Precious  Stones  :  their  Characters  and  Occurrence,''  by  Dr.  Max 
Bauer,  translated  by  L.  J.  Spencer,  M.A.  Griffin  &  Co.,  London, 
1904. 


92  PEECIOUS  STONES. 

reliable  test,  however,  seems  to  be  in  the  destruction  of  the 
stone.  The  real  Turquoise,  on  strongly  heating  in  the  blow- 
pipe flame,  decrepitates  violently  and  turns  brown  to  black. 
The  artificial  production  under  the  same  treatment  fuses 
quietly  to  a  black  glass. 

The  exact  method  of  their  preparation  is  not  known,  but 
seems  to  consist  in  applying  great  pressure  to  small 
quantites  of  powder  having  the  composition  of  Turquoise 
(hydrous  phosphate  of  alumina  with  a  trace  of  copper  oxide) ; 
the  powder  is  chemically  precipitated,  and  is  in  a  very  fine 
state  of  division.  The  stones  produced  by  this  method  are 
all  small,  no  large  ones  having  been  detected. 

With  increase  of  knowledge,  as  each  branch  of  science 
grows,  we  may  yet  live  to  see  the  day  when  Diamonds  will  be 
made  on  the  "  while  you  wait  "  system.  In  these  days  of 
scientific  marvels,  one  wonders,  not  at  what  has  been  done 
or  what  is  likely  to  be  accomplished  in  the  future,  but  what 
will  be  left  undone.  In  point  of  fact,  we  have  almost  ceased 
wondering  at  all. 

The  more  scientific  methods  of  identification  have  been 
mentioned  elsewhere,  so  no  mention  has  been  made  in  this 
chapter  of  specific  gravity  solutions,  refractometers,  or  the 
colouring  effects  of  radium  or  the  Eontgen  rays  upon  the 
Diamond  and  Sapphire. 


CHAPTER   VI. 

THE    DIAMOND. 

ALTHOUGH  this  mineral  is  not  referred  to,  so  far  as  can 
be  ascertained,  by  the  most  ancient  writers,  there  seems 
reason  to  believe  that  it  was  known  to  some  of  the  great 
princes  of  olden  times,  but  to  few  of  the  people.  Thus  Pliny 
says  it  "  was  long  known  to  none  but  kings,  and  to  but 
very  few  of  them."  The  first  authenticated  reference  to  it 
occurs  towards  the  end  of  the  Augustan  period,  when 
Manilius  speaks  of  it  as  the  Adamas.  The  term  Adamas 
had  been  used  previously  by  the  Greek  writers  for  any 
extremely  hard  substance.  Once  known,  it  seems  to  have 
immediately  become  the  most  coveted  of  stones.  Although 
doubt  has  been  cast  on  the  identity  of  Pliny's  Adamas  with 
Diamond,  his  description  would,  as  King  points  Out,  apply 
to  the  Diamond,  for  he  speaks  of  it  as  "  pointed  at  the  two 
extremities  as  though  two  turbines  "  (whipping  tops  of  the 
form  of  a  many-sided  pyramid)  "  were  joined  together  by 
their  broadest  ends."  The  name  Adamas  is  said  to  be 
derived  from  a  Greek  word  meaning  "  unconquerable," 
because  it  was  supposed  that  the  hardness  of  the  Diamond 
was  so  great  that  it  would  not  only  break  into  fragments 
the  hammer  with  which  it  was  struck,  but  would  also 
splinter  the  anvil  on  which  it  was  laid.  Further,  the 
greatest  heat  was  reputed  unable  to  make  the  stone  red 
hot.  As  already  mentioned,  its  external  application  to  the 


94  PKECIOUS  STONES. 

human  body  was  held  to  be  an  antidote  to  poisons,  and  a 
cure  for  enchantments  and  insanity.  Great  virtue  was 
ascribed  to  it  as  a  preservative  from  lightning  and  pestilence. 
In  the  mouth  it  had  the  effect  of  causing  the  teeth  to  drop 
out ;  but  one  quaint  writer  refutes  this,  on  the  ground  that 
he  had  known  it  used  in  powdered  form  to  clean  the  teeth — 
for  which  purpose  it  would  probably  be  very  efficient — while 
the  teeth  lasted.  But  taken  internally,  it  was  a  violent 
poison.  It  maintained  affection  between  man  and  wife. 

In  the  East  it  was  known  as  "  ripe  Diamond  "  or  "pakka," 
to  distinguish  it  from  the  "  unripe  Diamond  "  (kacha)  or 
Eock  Crystal. 

As  it  occurs  in  Nature  its  physical  characteristics  are  re- 
markable ;  in  colour  there  is  a  considerable  range.  The 
crystallised  variety  may  be  colourless,  or  of  a  peculiar 
steely  white  colour  in  the  most  sought-after  specimens,  but 
they  only  form  some  25  per  cent,  of  the  stones  found.  A 
similar  proportion  are  faintly  coloured,  and  quite  half  are 
more  or  less  dark  in  colour.  As  a  rule,  tbe  presence  of 
colouring  matter  detracts  from  the  value  of  the  stone,  but 
an  exception  is  made  when  the  colour  is  of  any  very  fine 
shade.  The  commonest  shades  found  are  honey-yellow, 
though  other  shades  of  yellow  are  frequently  found,  except 
sulphur-yellow.  Various  shades  of  green  are  the  next  most 
common,  but  as  a  rule  the  tint  is  a  dull  one,  and  only  in 
very  rare  cases  is  it  rich,  only  a  few  good  green  stones  being 
known,  and  most  famous  amongst  these  is  the  "  Dresden 
Green,"  a  gem  of  nearly  fifty  carats.  Various  shades  of 
grey  are  common,  but  black  is  rarely  seen  in  well  crystallised 
stones,  though  in  the  Bort  (vide  infra)  it  is  common.  Eed 
is  a  very  rare  shade,  too,  but  when  it  does  occur  the  tints 


PEECIOUS  STONES.  95 

are  usually  brighter.  A  ruby-red  Diamond  of  ten  carats  is 
said  to  be  amongst  the  Eussian  crown  jewels,  and  a  rose- 
red  one  of  three  times  this  size  belongs  to  Austria.  Blue 
is  the  rarest  shade  of  all.  It  may  occur  as  a  light  or  dark 
blue.  Probably  the  most  noted  stone  of  this  colour  is  the 
"  Hope  "  Diamond,  of  forty-four  carats. 

Brazil  seems  to  have  produced  most  of  the  coloured 
stones  of  note,  though  recently  a  fine  red  specimen  was 
obtained  in  Borneo. 

Many  Diamonds,  when  found,  are  coated  with  a  coloured 
film,  frequently  of  a  greenish  tinge.  This  is  particularly 
the  case  with  Brazilian  stones,  and  as  a  rule  is  found  only 
to  be  superficial,  so  that  by  cutting  a  perfectly  colourless 
stone  may  be  produced.  Some  of  the  South  African  stones 
are  "  smoky,"  especially  on  the  dihedral  and  solid  angles. 

The  lustre  of  well  crystallised  Diamonds  is  adamantine  in 
a  splendant  degree.  From  this  high  lustre  all  grades  may 
be  found  to  greasy  and  dull.  Water-worn  stones  often  show 
almost  a  metallic  lustre.  Crystals  are  usually  transparent, 
while  Bort  is  only  translucent,  and  Carbonado  is  opaque. 
The  degree  of  transparency  varies  greatly  with  the  condition 
of  the  surface.  Thus  water-worn  crystals  may  be  likened 
to  ground  glass — seemingly  translucent  only ;  but  if  their 
surfaces  be  polished,  as  in  the  process  of  cutting,  the  stone 
may  be  found  to  be  transparent  in  a  high  degree.  Stones 
which  show  more  than  a  certain  degree  of  cloudiness  cannot 
be  utilised  as  gems. 

The  refractive  index  is  high,  and  dispersion  is  very  high. 
Des  Cloizeaux  gives  the  following  value  of  n — 

Ked.  Yellow.  Green. 

2-4135  2-4195  2'4278 


96  PEECIOUS   STONES. 

The  difference  between  the  indices  for  the  B  and  H  lines 
of  the  spectrum  is  "0574,  which  figure  is  therefore  the 
coefficient  of  dispersion  in  Diamond. 

Since  the  "  fire  "  of  a  stone  depends  on  the  degree  to 
which  white  light  is  split  up  into  its  components,  it  at  once 
becomes  obvious  that  the  fire  of  this  gem  is  very  marked. 

Diamond,  being  a  cubic  mineral,  should  always  show 
single  refraction ;  but  this  is  not  always  found  to  be  the 
case,  anomalous  double  refraction  frequently  being  present, 
especially  in  stones  that  are  coloured,  or  contain  enclosures 
of  impurities.  It  is  found  that  many  crystals  of  Diamond 
show  signs  of  great  internal  strain,  so  great  at  times  that  a 
stone  will  sometimes  fly  to  pieces  on  being  handled.  This 
suggests  that  the  mineral  is  often  formed  under  conditions 
of  great  pressure.  Max  Bauer  quotes  the  similar  instance 
of  "  Prince  Rupert's  Drops,"  small  beads  of  glass  formed 
during  the  blowing  of  glass  vessels,  in  which  great  internal 
strain  is  set  up  on  cooling,  and  in  which,  too,  double 
refraction  is  seen,  due  to  this  strain,  although  glass,  being  a 
colloid  body,  should  only  show  single  refraction.  The 
smoky  stones  from  South  Africa  show  the  phenomenon  in 
the  most  marked  degree.  Under  the  polariscope,  with  the 
Nicol's  prisms  crossed,  a  stone  showing  single  refraction 
when  rotated  gives  a  complete  dark  field ;  but  specimens 
having  these  internal  strains  show  irregular  light  portions 
of  the  field  under  the  same  conditions.  Precautions  must 
of  course  be  taken  to  ensure  that  light  is  not  entirely  cut 
off  by  total  internal  reflection,  by  surrounding  the  stone  with 
some  highly  refractile  medium  during  examination. 
Diamond  occasionally  shows  asterism. 

Phosphorescence  is  strongly  marked  in  most  Diamonds, 


PEEOIOUS  STONES.  97 

but  is  not,  as  a  rule,  produced  to  any  marked  degree  by 
the  direct  act  of  light,  especially  in  the  case  of  larger  stones, 
though  smaller  ones  may  more  often  show  it;  when, 
however,  the  mineral  is  rubbed  on  cloth  or  paper,  most 
stones  are  found  to  become  phosphorescent,  though  the  light 
emitted  is  as  a  rule  not  strong,  and  does  not  last  for  any 
considerable  time ;  yellow  is  the  commonest  colour  shown. 
The  high  tension  electric  discharge  from  a  vacuum  tube 
causes  Diamond  to  phosphoresce. 

Under  X-rays,  Diamond  is  found  to  be  remarkably  trans- 
parent, a  Sapphire  appearing  quite  opaque  in  comparison ; 
thus  a  convenient  means  is  at  hand  for  examining  a  large 
parcel  of  stones,  other  substances  which  could  be  substituted 
for  Diamond  casting  a  shadow,  and  thus  discovering  any 
attempt  at  substitution. 

Under  the  influence  of  heat  no  change  is  observed  as  a 
rule  until  high  temperatures  are  reached,  though  a  few 
specimens  may  phosphoresce  on  heating,  but  all  have  this 
property  destroyed  by  great  heat.  Moissan  gives  the 
temperature  of  ignition  in  oxygen  as  690°  to  840°  C.,  but 
if  heated  out  of  contact  with  air  or  oxygen  no  change  occurs 
up  to  an  intense  white  heat,  and  then  only  a  very  slow  conver- 
sion into  the  aliotropic  form  of  carbon,  Graphite,  takes  place 
(vide  infra).  Diamond  is  a  good  conductor  of  heat;  hence  mois- 
ture rapidly  condenses  on  it  and  rapidly  evaporates  again. 

With  regard  to  its  electrical  behaviour,  Diamond  shows 
a  charge  of  positive  electricity  when  rubbed,  and  this 
whether  the  faces  are  in  the  natural  form  or  cut ;  it  is  of  a 
very  high  electrical  resistance,  a  fact  of  greater  interest 
since  other  forms  of  carbon,  as  Graphite  and  coke,  are  good 
conductors. 

p.s.  H 


98  PEECIOUS   STONES. 

The  specific  gravity  is  high  for  a  gem  stone,  that  of 
crystals  being  3'516  to  3*525 ;  the  variety  Carbonado  is, 
however,  rather  less  dense,  3*15 — 3'29,  while  Bort  is  almost 
the  same  as  the  crystallised  variety,  3*5. 

When  broken,  if  a  fracture  is  developed,  it  is  seen  to  be 
conchoidal,  but  cleavage  is  much  more  often  seen  than 
fracture. 

The  cleavage  of  Diamond  is  parallel  to  the  faces  of  the 
octahedron,  and  is  highly  perfect,  so  that  the  cleavage 
planes  appear  bright,  smooth  and  regular ;  cleavage  is 
obtained  with  great  ease  by  the  means  described  under 
gem-cutting,  and  use  is  very  frequently  made  of  this 
property  in  the  cutting  of  the  gem  into  brilliants,  since 
this  particular  shape  may  be  said  to  be  derived  from  a  regular 
octahedron.  Hence,  whatever  the  external  form  of  a  rough 
Diamond,  if  it  is  a  single  crystal  or  a  portion  of  one,  it  can 
be  reduced  easily  to  a  suitable  form  for  cutting.  In  cases 
where  no  actual  crystal  faces  are  to  be  seen  on  the  rough 
stone  a  careful  examination  will  usually  reveal  some  of  the 
octahedral  cleavage  planes,  and  thus  we  can  determine  in 
what  direction  the  remaining  planes  of  the  octahedron  may 
be  produced.  To  recognise  these  planes  when  unequally 
developed  requires  some  practice,  and  it  is  well  worth  while 
to  obtain  some  lumps  of  Fluor  Spar,  which  has  the  same 
cleavage,  and  to  practice  the  recognition  of  existing  cleavages 
and  the  production  of  fresh  ones  on  this  cheap  material, 
which  can  easily  be  obtained  in  single  crystals  the  size  of 
one's  fist.  Twinned  crystals  of  Diamond  cannot  be  cleaved 
into  an  octahedron  by  simple  cleavage. 

In  hardness  Diamond  exceeds  all  other  known  substances, 
and  on  Mohs'  scale  it  is  therefore  numbered  10.  The 


PRECIOUS  STONES. 


99 


crystallised  varieties  are  not  the  hardest,  as  Bort  and 
Carbonado  may  slightly  exceed  them.  Crystals,  too,  vary 
somewhat  in  hardness  in  different  directions,  probably  more 
so  in  specimens  showing  strain  than  in  others,  but  there  is 
a  fairly  constant  difference  in  the  direction  of  the  crystallo- 
graphic  axes,  the  hardness  being  greater  along  the  axes 
than  along  the  intermediate  directions.  Different  faces  of 
the  crystals,  too,  vary  in  hardness,  and  the  exterior  of  a 
crystal  is  usually  harder  than  the  interior.  Crystals  from 
various  localities  differ :  thus 
the  Australian  stones  are 
remarkably  hard,  and  the 
South  African  ones  relatively 
soft,  especially  before  they 
have  been  long  exposed  to 
'the  air. 

With  regard  to  frangibility, 
it  may  be  noted  that  the  old 
idea  that  a  Diamond  would 
splinter  the  anvil  on  which  it 
was  laid  to  be  broken  is 
erroneous,  for  on  the  contrary 
it  is  a  mineral  easily  reduced  to  powder  by  a  steel  pestle 
and  mortar. 

CRYSTALLINE  FORM,  OCCURRENCE,  AND  GENESIS. 
Diamond  crystallises  in  the  cubic  system,  and  although 
the  number  of  known  crystal  forms  is  not  great,  there  may 
yet  be  an  enormous  number  of  planes  on  a  natural  crystal, 
since  some  of  these  forms,  when  complete,  may  be  composed 
of  as  many  as  forty-eight  planes  or  faces.  The  "  habit  " 

H  2 


FIG.  9. — Diamond  :  A  Natural 
Crystal. 


100 


PEECIOUS  STONES 


of  the  crystal,  too,  varies  considerably,  though  most  com- 
monly the  octahedral  forms  predominate  (Fig.  9) ;  twin 
crystals  are  often  seen,  both  of  the  contact  and  interpene- 
tration  types.  By  suppression  of  alternate  faces  of  the 


FIG.  10. — Drawings  of  Crystals  of  Diamond. 

octahedron,  forms  of  the  regular  tetrahedron  arise.  The 
plane  of  twinning  is  parallel  to  the  octahedron,  and  the 
twins  are  often  flattened  parallel  to  the  same  form  so  as 
to  have  the  general  appearance  of  basal  slices  of  two 
triangular  pyramids  applied  to  one  another.  The  faces  are 


PRECIOUS  STONES. 


101 


commonly  curved ;  the  true  explanation  of  this  is  a  matter 
of  uncertainty.  The  great  majority  of  minerals  which  are 
found  crystallised  occur  bounded  by  true  planes,  but  on  the 
other  hand  a  few,  and  prominent  amongst  these  few  is  the 


FIG.  11. — Drawings  of  Crystals  of  Diamond. 

Diamond,  are  more  often  found  in  curved  forms.  Still  more 
interesting  perhaps  is  the  fact  that  certain  crystallised 
minerals  may  have  the  majority  of  their  surfaces  quite  flat, 
yet  some  one  or  two  crystal  forms  of  the  same  mineral  may 
almost  constantly  be  found  curved ;  the  writer,  in  the 


102  PEEOIOUS  STONES. 

examination  of  many  thousands  of  crystals  of  Barytes, 
has  invariably  found  one  or  two  crystal  forms,  when  present, 
to  be  curved,  and  this  in  a  mineral  that  may  show  over 
thirty  forms  on  one  crystal,  all  the  others  being  remarkably 
flat.  This  would  rather  suggest  that  the  curvature,  which  is 
undoubtedly  developed  at  the  time  of  the  growth  of  the 
crystal,  is  due  not  so  much  to  the  surrounding  conditions  as 
to  some  special  surface  force  acting  on  particular  planes  of 
the  crystal  in  a  much  greater  degree  than  on  others.  This 
curving  of  the  faces  may  in  some  types  of  crystal  lead  to 
an  almost  spherical  form,  as  in  No.  5  of  the  drawings  from 
the  Eaith  collection  (Figs.  10  and  11)  ;  again,  it  leads  to 
great  difficulty  in  the  exact  measurement  of  the  angles  on 
Diamond  crystals,  and  for  this  reason  the  interesting  ques- 
tion of  the  exact  group  of  symmetry  to  which  the  mineral 
belongs  is  still  unsettled.  Another  characteristic  of  the 
crystals  is  the  presence  of  numerous  striations  on  some  of 
the  faces,  usually  parallel  to  the  intersection  with  the  octa- 
hedron. Two  crystal  forms  show  characteristic  markings 
on  their  faces  :  thus  the  cube  faces  have  little  depressions, 
as  if  a  truncated  four-sided  pyramid  had  been  pressed  into 
them  smaller  end  first;  the  faces  of  the  octahedron,  too, 
show  sunk  triangular  pits  with  the  triangular  outline 
inverted  in  relation  to  the  outline  of  the  octahedral  face. 

Although  Diamond  crystals  are  as  a  rule  idiomorphic,  this 
is  not  invariably  the  case,  some  being  found  impressed  by 
other  crystals,  such  as  Quartz  ;  inclusions  of  a  mineral 
which  is  very  likely  Chlorite,  and  more  rarely  of  Haematite, 
occur ;  some  crystals  contain  innumerable  minute  cavities  ; 
Diamond  also  occurs  included  in  Quartz  and  Anatase. 

Crystals   of    cubic  habit  are  most  frequently  found   in 


PRECIOUS  STONES.  103 

Brazil ;  the  rhombic  dodecahedron  is  also  seen  in  Brazilian 
specimens ;  crystals  from  the  Urals  usually  show  the  four- 
faced  cube  according  to  Parrot ;  Indian  and  South  African 
crystals  are  more  frequently  octahedral  in  habit,  though 
not  necessarily  having  the  octahedral  face  itself  largely 
developed. 

The   variety  of   Diamond  known  as   Bort  (also  spelled 
Boort  and  Boart)  occurs  in  rounded  forms,  having  a  con- 
fused crystalline  structure,  and  hence  no  definite  external 
crystallised  form,  and  no  definite  cleavage.     In  colour  it  is 
usually   grey   or   black,  the  lustre   is  greasy,  the   specific 
gravity  less  than  of  the  crystallised  variety  and  the  hard- 
ness slightly  greater.     There  seems  to  be  a  regular  grada- 
tion from  one  of  these  varieties  to  the  other,  and  also  from 
Bort  to  Carbonado.     Although  useless  as  a  gem,  Bort  is  very 
valuable  for  many  technical  purposes  which  will  be  men- 
tioned later.     In  the  Diamond  trade  not  only  is  the  term 
used  as  here,  but  any  specimen  of  the  crystallised  variety 
which  by  reason  of  bad  colour,    flaws,   deficient  size,  or 
other  cause,  is  unfit  to  cut,  is  included  under  the  term  Bort. 
Carbonado  is  the  same  mineral  in  a  still  more  confused 
state  of  aggregation ;  frequently  it  is  called  Black  Diamond, 
but  as  under  that  term  it  might  be  confused  with  the  black 
varieties  of  the  true  Diamond,  it  is  better  to  adhere  to  the 
mineralogical  term.     Carbonado  may  be  granular,  or  quite 
compact ;  it   shows   no   cleavage.      Its  hardness  may  be 
greater  than  Diamond  in  crystals,  but  it  is  less  brittle,  and 
thus  is  also  largely  used  in  technical  processes.     Its  specific 
gravity  is  less  than  Diamond  proper,  possibly  due  to  some 
degree  of  porosity.      It  chiefly  comes  from  the   Serra  da 
Cincora,  in  the  state  of  Bahia  in  Brazil,  where  it  is  found  in 


104  PEEOIOUS  STONES. 

considerable  masses — up  to  731  carats,  according  to 
E.  Boutan.  It  has  here  been  found  enclosing  Diamond. 

The  origin  of  Diamond  has  for  ages  been  a  point  of 
dispute,  and  innumerable  theories  have  been  advanced 
dealing  with  the  subject.  One  of  the  difficulties  is  that  in 
most  cases  the  mineral  is  not  found  in  situ,  but  only  in 
alluvial  deposits,  either  recent  or  ancient,  containing  the 
debris  of  many  different  rocks,  as  a  rule. 

The  earliest  definite  theory  advanced  was  that  of  Brewster, 
who  held  the  mineral  to  be  formed  by  the  consolidation  of 
a  resinous  substance  resulting  from  plant  life.  Jameson 
held  it  to  be  a  separation  product  from  sap.  Later  a  large 
number  of  scientists  regarded  it  as  certain  that  the  carbon 
came  from  the  decomposition  of  organic  matter,  either  vege- 
table or  animal,  but  they  were  divided  as  to  the  means  by 
which  carbon  in  its  ordinary  organic  combinations  could  be 
transformed  into  the  allotropic  form  Diamond,  some  hold- 
ing that  a  very  high  temperature  was  necessary,  and 
others  that  the  change  could  be  accomplished  at  compara- 
tively low  temperature.  Of  the  latter  group,  D'Orbigny  and 
Wohler  were  some  of  the  first  thinkers.  Later,  when  it 
became  known  from  experimental  work  that  Graphite,  and 
not  Diamond,  was  formed  by  the  action  of  great  heat  on 
amorphus  carbon,  there  were  several  who  held  to  the  low 
temperature  theory,  among  these  G.  Bischof.  J.  D.  Dana, 
of  the  former  group,  believed  it  to  result  from  the  alteration 
of  carbonaceous  matter  by  processes  then  invoked  to 
account  for  the  metamorphism  of  rocks.  Parrot  believed 
the  change  to  occur  from  the  sudden  cooling  of  highly 
heated  organic  matter,  and  Carvill  Lewis,  from  a  study  of 
the  South  African  deposits,  came  to  the  conclusion  that  the 


PRECIOUS  STONES.  105 

Diamond  was  there  formed  in  the  rock  in  situ  at  the  time  of 
its  consolidation  from  the  molten  condition,  and  that  the 
carbon  was  derived  from  the  carbonaceous  shales  caught  up 
in  the  molten  mass  during  its  intrusion.  C.  von  Leon- 
hard  thought  it  arose  as  a  sublimation  product.  Liebig 
believed  various  products  were  formed,  ever  growing  richer 
in  carbon,  and  from  the  final  substances  pure  carbon 
crystallised  out  as  Diamond.  Others  held  its  formation  to 
be  due  to  the  decomposition  of  a  gaseous  hydrocarbon  or 
of  carbon  dioxide.  Simmler  suggested  that  carbon  was 
soluble  in  carbon  dioxide  under  great  temperature  and 
pressure,  deriving  this  idea  seemingly  from  the  presence  in 
Diamond  of  liquid  carbon  dioxide  in  minute  cavities.  St. 
Clair  Deville  advocated  an  origin  from  halogen  compounds 
of  carbon.  Sorby  felt  that  the  presence  of  carbon  dioxide 
in  the  cavities  was  irreconcilable  with  the  association  of 
more  than  a  very  little  water  in  the  formation. 

Any  consideration  of  the  subject  must  necessarily  take 
into  account  the  modes  of  occurrence  at  the  various  localities, 
so  it  may  be  convenient  to  briefly  consider  here  where  and 
under  what  conditions  Diamond  is  found. 

By  far  the  most  important  locality  at  the  present  day  is 
South  Africa,  for  this  region  now  produces  at  least  nine- 
tenths  of  the  total  output.  The  discovery  of  Diamond  there 
only  took  place  in  1867,  and  the  exact  circumstances  are 
variously  given.  According  to  the  more  general  story,  the 
child  of  a  Boer,  named  Jacobs,  was  seen  playing  with  some 
bright  stone  picked  up  in  the  neighbourhood.  A  visitor  to 
the  house,  named  Schalk  van  Niekerk,  saw  it  and  offered  to 
purchase  it,  as  it  seemed  peculiar  to  him,  but  his  host 
insisted  on  making  him  a  gift  of  it.  Van  Niekerk,  according 


106  PEECIOUS  STONES. 

to  this  version,  handed  the  stone  to  O'Reilly  for  identifica- 
tion, and  the  latter  pronounced  it  to  be  a  Diamond;  it 
weighed  rather  more  than  21  carats.  The  other  version 
states  that  the  stone  passed  to  O'Reilly  from  Jacobs,  and  that 
O'Reilly  sent  it  to  Dr.  Atherstone,  of  Grahamstown,  who 
identified  it  by  scientific  tests.  Be  that  as  it  may,  the 
Diamond  was  found  near  Hopetown,  in  Cape  Colony.  It 
was  sent  to  the  Paris  Exhibition  of  1867,  and  afterwards 
purchased  by  the  Governor  of  Cape  Colony  for  £'500. 
Careful  search  by  the  settlers  of  the  district  brought  to 
light  more  stones,  and  next  year  workings  on  the  Vaal  river 
added  to  the  number.  Up  to  the  end  of  1870,  these  river 
workings  were  the  only  ones  that  were  productive.  The 
stones  were  found  chiefly  in  the  Vaal  about  Barkly  West, 
some  occurring  in  the  gravel  in  the  bed  of  the  stream,  and 
often  quite  a  number  being  found  in  the  "  pot-holes," 
eroded  by  the  river  setting  stones  whirling  round  in 
its  bed.  It  was  also  found  that  the  old  river  terraces 
bordering  on  the  present  bed  yielded  Diamonds,  even  to  a 
height  of  200  feet  above  the  present  level.  Specimens  were 
found  as  far  up  as  Christiana,  in  the  Transvaal,  though  the 
lower  workings  were  most  productive.  Since  the  stones 
occurred  amongst  water-worn  material,  and  themselves 
showed  signs  of  such  erosion,  it  is  obvious  that  they  have 
been  transported  some  distance  by  the  stream ;  the  gem  is 
associated  with  other  minerals,  such  as  Quartz,  and  several 
varieties  of  Chalcedony,  Garnet  and  Ilmenite.  In  quality 
these  "  river-stones  "  are  good,  and  hence  they  command  a 
price  above  that  obtained  for  stones  from  the  "  dry  diggings," 
to  be  mentioned  next. 

At  the  end  of  1870,  some  chance  discoveries  of  Diamonds 


PRECIOUS  STONES.  107 

on  the  farm  of  Du  Toit's  Pan  led  to  the  opening  up  of  the 
mine  now  known  by  that  name,  and  soon  there  was  a  rush. 
This  discovery  was  followed  by  another  close  by,  on  the 
site  now  occupied  by  Kimberley ;  this  was  the  famous  De 
Beers'  mine.  In  all  there  are  now  four  large  deposits  close 
to  the  town.  Two  other  deposits  were  also  found  south- 
south-east  of  Kimberley,  namely,  the  Koffyfontein  and  Jagers- 
fontein  mines,  in  what  is  now  the  Orange  Kiver  Colony. 
A  very  important  deposit  has  more  recently  been  found  at 
the  New  Premier  mine,  near  Pretoria,  from  which  the  famous 
Cullinan  Diamond  was  obtained. 

There  was  little  on  the  surface  to  mark  the  position  of 
these  deposits  around  Kimberly ;  some  of  them  were  slightly 
raised  above  the  surrounding  country,  some  showed  a  slight 
depression.  When  they  came  to  be  worked,  however,  it  was 
soon  seen  they  were  anything  but  surface  deposits,  as  at 
first  supposed,  for  the  material  in  which  the  Diamonds  were 
found  was  utterly  unlike  the  neighbouring  rock,  from  which, 
moreover,  it  was  separated  by  a  sharp  line  of  demarcation. 
This  surrounding  rock  consists  of  beds  of  the  Karoo  forma- 
tion. Under  a  layer  of  reddish  earth  is  a  bed  of  calcareous 
tufa  which  has  evidently  been  deposited  long  subsequent  to 
the  formation  of  the  material  in  which  the  Diamonds  are 
found,  and  therefore,  too,  later  than  the  Karoo  beds,  which 
are  themselves  of  comparatively  recent  geological  age, 
belonging  as  they  do  to  the  time  of  the  New  Eed  Series. 
The  Karoo  beds,  as  seen  in  the  Kimberley  mine,  consist  of  a 
layer  of  shale,  varying  in  colour  from  a  greenish  tint  above 
to  yellowish  below  ;  an  intrusive  sheet  of  dolerite  of  late 
Karoo  age  follows,  and  with  the  shales  makes  up  a  thick- 
ness of  50  feet.  Below  this  comes  a  bed  of  black  shales 


108  PRECIOUS  STONES. 

some  250  feet  in  thickness  ;  the  black  colour  is  due  in  part 
to  carbonaceous  matter  and  in  part  to  disseminated  Pyrites, 
as  is  the  case  in  many  of  the  black  shales  of  carboniferous 
age  in  England.  Below  this  again  is  a  layer  of  somewhat 
decomposed  basic  volcanic  rock  containing  amygdules,  of 
394  feet.  Lower  still  comes  a  400  foot  bed  of  quartzite,  and 
under  that  is  another  260  feet  of  black  shales ;  both  the 
quartzite  and  the  black  shales  are  penetrated  by  dolerite 
dykes.  The  general  disposition  of  these  rocks  is  horizontal, 
or  nearly  so,  except  near  the  pipe,  where  a  dip  away  from 
the  vent  is  sometimes  seen.  Below  the  lower  shales  there  is 
over  1,000  feet  of  quartz-porphyry  in  the  Kimberley  mine. 
The  Diamond-bearing  ground  consists  of  a  mass  of 
irregular  fragments  of  rock  of  various  shapes  and  sizes, 
usually  with  more  or  less  angular  outline,  and  consisting 
not  only  of  the  shales  and  basic  volcanic  rock  from  the  sur- 
rounding Karoo  beds,  but  also  of  rocks  not  seen  in  the 
neighbourhood ;  some  blocks  belonging  to  the  Middle 
Karoo  sandstones,  blocks  of  ultrabasic  rock  called  eclogite, 
masses  of  mica  schist,  and  pieces  of  granite.  Some  of  these 
masses  may  contain  many  thousand  cubic  yards  of  material, 
others  are  minute  splinters,  and  every  gradation  is  found 
between  these  extremes.  All  these  fragments  are  embedded 
in  a  bluish-green  material  consisting  largely  of  a  hydrous 
magnesium-iron  silicate,  with  some  carbonate  of  calcium. 
The  whole  mass  has  a  general  bluish  tinge,  except  near  the 
surface,  due  to  the  dissemination  of  this  material,  and  from 
this  appearance  it  has  been  named  "  blue-ground."  Where 
this  has  been  exposed  to  the  weathering  influence  of  sur- 
face water,  that  is  for  a  depth  of  50  or  60  feet,  the  process 
of  oxidation  has  converted  some  of  the  ferrous  compounds 


PEECIOUS  STONES.  109 

into  ferric,  with  the  result  that  the  colour  is  yellow  instead 
of  bluish,  and  this  upper  weathered  portion  is  therefore 
known  as  "yellow-ground."  At  the  point  of  junction  of 
yellow-ground  and  blue-ground  there  is  sometimes  a  tran- 
sitional layer  of  "  rusty-ground,"  marking  a  lower  stage  of 
oxidation. 

On  carefully  examining  this  mass  of  Diamond-bearing 
material,  we  find  it  is  roughly  in  the  shape  of  a  tube.  The 
Kimberley  mine  "  pipe  "  has  the  form  of  an  inverted  coach- 
ing horn.  In  other  words,  the  plan  on  the  surface  is  circular 
in  general  outline,  and  at  successively  lower  levels  the  cross 
section  becomes  less,  though  it  decreases  at  a  slower  rate  as 
the  depth  becomes  greater.  In  all  the  mines  the  surround- 
ing rock  abuts  suddenly  against  the  mass,  often  with  the 
beds  turned  upwards  next  the  pipe,  separated  only  by  slight 
fissures  filled  with  secondary  minerals,  if  separated  at  all. 
Thus  the  material  is  filling  a  huge  "  pipe  "  of  unknown 
depth  and  of  a  surface  diameter  varying  from  200  to  700 
yards  in  the  different  pipes.  There  seems  little  doubt  that 
the  material  filling  these  pipes  consists  of  the  larger  frag- 
ments ejected  by  an  ancient  volcano  into  the  air,  thence  to 
fall  back  again  into  the  throat  or  vent  along  with  a  certain 
amount  of  finer  volcanic  dust  and  probably  large  quantities 
of  water  condensed  from  the  steam  accompanying  the 
eruption  ;  this  volcanic  origin  of  the  pipes  was  first  sug- 
gested by  Cohen  in  1872.  The  bell-mouth  of  the  pipe  in 
the  Kimberley  mine  suggests  that  no  very  great  thickness  of 
rock  overlaid  the  present  surface  at  the  time  the  volcano 
was  active,  so  in  that  case  almost  certainly  all  the  "foreign" 
rocks  contained  in  the  pipes  are  from  below,  and  in  the 
other  cases  there  is  a  probability  that  they  are  also  rocks 


110  PEECIOUS  STONES. 

from  lower  strata.  Such  a  mass  of  volcanic  material  is 
called  an  agglomerate,  and,  as  is  not  infrequently  the  case 
in  other  agglomerates,  it  shows  signs  of  more  than  one  out- 
burst of  volcanic  activity,  for  the  whole  mass  is  sub-divided 
in  several  of  the  mines  into  vertically  columnar  portions 
which  seem  to  mark  a  later  eruption,  which  has  resulted  in 
the  material  already  choking  the  vent  being  broken  through 
and  a  fresh  vent  being  formed,  to  be  itself  afterwards 
choked  up.  Much  of  the  matrix  material  must  originally 
have  consisted  of  a  ferro-magnesian  silicate  by  the  hydro- 
metamorphism  or  thermo-metamorphism  of  which  the 
serpentinous  minerals  have  originated.  It  is  entirely  in 
this  blue  ground  that  the  Diamonds  occur,  none  ever  having 
been  found  in  the  surrounding  rock. 

In  the  De  Beers  mine  a  dyke  some  five  feet  thick 
traverses  the  blue  ground  in  a  sinuous  path,  and  is  hence 
known  as  the  "  snake  rock."  It  is  of  much  the  same  com- 
position as  the  blue  ground,  but  contains  no  Diamonds.  In 
the  South  African  Museum  there  is  a  specimen  of  dyke  from 
the  blue  ground  of  the  De  Beers  mine,  which  shows  good 
crystals  of  Olivine  in  a  ground  mass  of  Perofskite,  Magnetite, 
and  Calcite.  The  occurrence  of  Diamond  in  agglomerate 
near  Pretoria  is  of  interest,  as  here  the  geological  horizon 
is  far  below  the  carbonaceous  shales  (Molengraaff). 

The  associated  minerals  in  the  Kimberley  district  consist 
of  a  large  variety  of  species,  chief  among  which  in  point  of 
abundance  are  Garnet,  Enstafcite,  and  altered  Mica.  The 
Garnet  is  of  the  variety  Pyrope,  and  occurs  in  broken 
fragments,  often  fresh,  but  sometimes  partly  decomposed 
Chromium  is  always  present  in  it.  The  Enstatite  is  often 
found  enclosing  Garnet.  Amongst  other  minerals  of  less 


PKECIOUS  STONES.  Ill 

frequent  occurrence,  but  in  some  cases  of  greater  interest 
from  the  point  of  view  of  the  origin  of  the  Diamond,  are 
Diallage,  Tremolite,  Wollastonite,  Ilmenite,  Magnetite, 
Chromite,  Zircon,  Sapphire,  Topaz,  Tourmaline,  and  Eutile. 

Other  minerals  of  more  recent  secondary  origin,  as  Calcite 
and  some  of  the  Zeolites,  are  found,  but  they  are  of  much 
less  importance  in  the  present  respect.  The  Diamonds  them- 
selves occur  either  in  crystals  or  in  broken  fragments,  often 
in  cleavage  octahedra. 

India  for  long  furnished  the  whole  output  of  Diamonds, 
but  to-day  the  case  is  very  different.  Still,  the  localities 
where  the  mineral  has  occurred  are  numerous,  and  have 
furnished  some  of  the  most  interesting  data  for  considera- 
tion with  regard  to  the  origin  of  the  gem.  When  the 
Diamond  was  first  found  in  India  is  not  known,  but  Ptolemy 
refers  to  its  occurrence  there. 

The  famous  Golconda  mines  are  really  far  from  the  place 
of  that  name,  being  situated  in  various  groups,  distant 
100  to  200  miles  to  the  south  and  east  of  Golconda.  The 
most  southern  of  these  mines  are  along  the  Penner  river, 
and  to  the  south  of  Karnul,  and  between  it  and  the  Penner 
is  another  series.  To  the  north-east  again,  on  the  Kistna 
river,  are  the  mines  of  Kollur,  whence  are  supposed  to  have 
come  the  Koh-i-Noor,  the  blue  "  Hope  "  Diamond,  and  the 
Great  Mogul.  In  all  these  mines  the  mineral  occurs  in 
some  derived  rock,  sometimes  in  a  loose  sand,  as  at  Kollur 
and  Partial,  or  in  alluvium,  as  at  the  Chennur  mines.  At 
the  mines  to  the  south  of  Karnul  the  Diamond  occurs  in  a 
bed  of  conglomerate  of  fragments  derived  from  shales  and 
Lydian-stone,  only  a  few  inches  thick.  At  Muleli,  between 
the  rivers  Kistna  and  Godavari,  the  rock  containing  the 


112  PEECIOUS  STONES. 

Diamonds  is  also  composed  of  the  cemented  detritus  of 
other  rocks. 

But  at  Wajra  Karur,  near  Bellary,  in  north  lat.  15°  and 
east  long.  77°,  where  the  Diamonds  are  often  found  lying 
loose  on  the  surface  after  a  rain,  a  much  more  interesting 
and  instructive  mode  of  occurrence  is  recorded.  Chaper, 
("  Comptes  Kendus,"  vol.  xcviii.,  1884),  a  French  traveller, 
states  that  he  himself  found  two  Diamonds  in  this  neigh- 
bourhood in  1882,  in  some  of  the  pegmatite  veins,  with 
Epidote,  traversing  the  gneiss  which  underlies  the  soil  here. 
The  Diamonds  were  associated  with  Ruby  and  Sapphire.  It 
has  been  suggested  that  Chaper  was  deceived  by  his 
native  attendant,  and  that  the  associated  Corundum 
showed  signs  of  workmanship.  As  Max  Bauer  points 
out,  the  association  of  Diamond  with  Corundum  and 
Epidote,  is  met  with  elsewhere  in  India,  and  the 
detrital  rocks  in  which  the  mineral  occurs  in  these 
other  localities  may  possibly  have  originated  from  the 
disintegration  of  a  rock  similar  to  the  gneiss  of  Wajra 
Karur.  To  the  west  of  this  town  a  pipe  of  material  similar 
to  the  agglomerate  of  Kimberley  was  found,  but  it  yielded 
no  Diamonds.  Still,  many  similar  pipes  in  South  Africa 
have  shown  no  signs  of  this  gem. 

Some  400  miles  to  the  north-east  of  the  Kollur  group  of 
mines  there  are  found  many  deposits  in  the  Mahanadi 
river,  chiefly  in  its  upper  part.  This  river  has  been  by 
some  identified  with  the  river  mentioned  by  Ptolemy.  The 
Mahanadi  deposits  occur  in  the  sand  and  gravel  brought 
down  by  the  river,  so  the  only  light  thrown  on  the  origin  of 
the  mineral  is  what  is  derived  from  a  consideration  of  the 
associated  minerals.  These,  besides  Quartz  and  some 


PKECIOUS  STONES.  113 

varieties    of     Chalcedony,     include     Garnet,    Beryl,    and 
Topaz. 

Other  deposits  in  river  gravel  occur  about  200  miles 
south-west  of  the  previous  group  at  Wairagarh ;  also  100 
miles  north-east  to  200  miles  north-north-east  of  the 
Mahanadi  deposits,  near  Jushpur,  and  about  Sumelpur. 
Many  of  these  seem  to  have  been  of  considerable  importance 
at  the  time  Tavernier  visited  them  (1560),  but  now  they 
are  not  of  great  interest  as  productive  deposits. 

A  large  group  of  deposits  extends  south-west  from 
Allahabad  for  150  miles  or  so,  and  is  known  as  the  Panna 
group.  At  none  of  these  Panna  mines  is  the  mineral 
actually  found  in  the  rock  in  which  it  was  developed.  In 
some  of  the  workings  it  occurs  in  thin  beds  of  detrital 
rocks  of  great  age ;  in  others,  again,  simply  in  sands  and 
gravels  derived  from  a  further  disintegration  of  these 
detrital  rocks.  Only  at  Birjpur  has  the  material  been 
cemented  into  a  firm  conglomerate.  The  associated 
minerals  do  not  seem  to  be  of  special  interest,  consisting 
only  of  siliceous  minerals  in  most  cases. 

In  the  early  part  of  the  eighteenth  century  Diamonds  were 
found  in  Brazil  in  the  gold  washings  in  the  State  of  Minas 
Geraes,  though  not  definitely  recognised  as  such  until  they 
came  into  the  hands  of  the  Dutch  consul  at  Lisbon.  They 
are  usually  said  to  have  been  found  first  a  short  distance  to 
the  west  of  Tejuco,  a  town  which  afterwards  became  known 
as  Diamantina,  lying  some  340  miles  north  of  Kio  de  Janeiro. 
The  mineral  is  found  under  different  conditions  in  the 
various  kinds  of  workings,  but  the  most  important  from  the 
point  of  view  of  the  origin  of  the  mineral  are  what  are 
known  as  "  plateau  workings.2'  These  occur  on  the  high 
p.s.  i 


114  PEECIOUS  STONES. 

ground  around  Diamantina  at  a  height  of  4,000  feet  above 
sea  level.  A  mountain  chain,  the  Serra  do  Espinha9o, 
running  generally  north  and  south,  ends  in  this  high  ground 
of  the  plateau  ;  the  surface  rock  is  a  thinly  laminated  sand- 
stone containing  flakes  of  a  green  Mica.  It  has  the  peculiar 
property  of  flexibility,  just  as  some  of  the  Indian  sandstones 
have,  and  much  interest  would  attach  to  a  microscopic 
examination  of  this  rock  to  determine  the  shape  of  the  sand 
grains.  In  places  the  rock  is  of  a  coarser  nature,  more 
approaching  a  conglomerate.  The  age  of  the  stratum  is 
not  definitely  known,  but  is  almost  certainly  of  considerable 
geological  antiquity  ;  from  its  extensive  occurrence  in  the 
Serra  Itacolumi  it  is  generally  spoken  of  as  itacolumite  ; 
it  is  interbedded  with  schists  in  which  Hornblende,  Haema- 
tite, and  Mica  are  developed.  This  is  a  point  of  great 
importance,  for  it  points  to  the  rocks  having  undergone 
considerable  metamorphism.  Underlying  these  rocks  are 
others  described  as  gneiss  ;  the  itacolumite  and  the  schists 
are  penetrated  by  "  veins"  containing  a  good  deal  of  Quartz. 

Where  the  rivers  have  cut  through  layers  of  Diamond- 
bearing  rock  the  gem  is  found  in  thin  beds,  often  for  a  con- 
siderable distance ;  thus  the  Eio  Jequetinhonha  and  its 
tributaries  have  Diamond-bearing  gravels  as  far  down  as 
Mendanha,  though  the  tributaries  coming  in  from  the 
plateau  to  the  west  are  most  productive.  Other  streams 
which  do  not  cut  these  rocks  yield  no  Diamonds,  as,  for 
instance,  the  Kio  Doce. 

The  gravels  worked  in  the  present  river  beds  are  the 
"  river  deposits."  It  is  found  that  the  larger  Diamonds 
occur  in  the  upper  part  of  the  stream,  while  lower  down  the 
stones  are  smaller.  This  is  as  one  would  expect,  for  not 


PEECIOUS  STONES.  115 

only  would  a  substance  of  a  moderately  high  density  such 
as  the  Diamond  be  difficult  to  move  by  any  but  more 
rapidly  running  water,  but  also  transportation  over  many 
miles  of  country  would  mean  a  considerable  reduction  in 
size  even  to  the  Diamond.  As  in  South  Africa,  the  pot-holes 
in  the  river  beds  are  often  found  to  yield  a  large  number  of 
the  stones. 

What  are  known  as  "  valley  deposits  "  are  very  similar  to 
the  river  deposits,  except  that  they  represent  much  older 
detrital  matter  carried  down  by  the  stream  when  its  bed 
was  at  a  higher  level  than  now.  This  detritus  is  now  left 
along  the  banks  in  the  old  river  terraces.  In  some  cases 
material  of  this  kind  is  found  to  have  been  re-cemented 
into  a  conglomerate. 

The  "plateau  deposits"  near  Diamantina  consist  of  large 
broken  fragments  of  the  rocks  from  the  district  around, 
embedded  in  a  red  earthy  ground  mass.  This  mass  is 
known  locally  as  "  gurgulho."  A  noteworthy  point  is  that 
the  rock  fragments  are  angular,  or  only  very  slightly 
rounded,  suggesting  an  origin  similar  to  that  of  the 
"brockram  "  of  the  New  Red  Series  in  England. 

Some  distance  to  the  west  of  Diamantina,  at  Sao  Joao 
da  Chapada,  the  Diamonds  occur  in  a  very  peculiar  plateau 
deposit,  lying  in  great  trenches  of  over  100  feet  in  depth, 
and  twice  that  in  width,  and  several  hundred  yards  long. 
These  trenches  are  filled  with  alternating  beds  of  clay  and 
itacolumite;  the  beds  are  well  marked  and  have  a  pro- 
nounced inclination  to  the  east.  Penetrating  these  beds  are 
"veins"  containing  Quartz,  Haematite,  and  Kutile.  Other 
minerals  in  association  with  the  Diamond  are  Tourmaline, 
Anatase,  and  oxides  of  iron.  All  the  minerals  are  found  in 

i  2 


116  PKECIOUS  STONES. 

crystals  without  any  sign  of  erosion,  and  it  has  been  noticed 
that  where  these  associated  minerals  are  more  abundant  the 
Diamond  is  more  common  also. 

Gorceix  ("  Comptes  Kendus,"  vol.  xciii.,  1881),  has  been  led 
to  conclude  from  an  examination  of  this  deposit  that  the 
Diamonds  here  occur  in  situ,  that  they  have  actually  been 
formed  in  the  Quartz  "  veins  "  which  so  frequently  penetrate 
the  rocks  here.  So  far  no  Diamonds  have  actually  been 
seen  in  the  "veins,"  though  they  have  been  found  adhering 
to  Quartz  and  to  the  other  minerals  occurring  in  the 
"  veins." 

One  cannot  but  wish  more  definite  information  was  avail- 
able as  to  this  deposit,  especially  as  to  the  geological  history 
of  the  trench  and  its  contents  and  their  relation  to  the 
surrounding  rocks,  the  past  physical  history  of  the  district, 
and  most  particularly  the  relation  of  the  "  veins  "  to  the 
rocks  they  penetrate. 

At  Bagagem,  some  200  miles  west  of  Diamantina,  in  the 
Serra  dos  Pilons,  are  other  deposits,  famous  as  having 
yielded  in  1853  the  Star  of  the  South,  a  fine  stone  of 
254 J  carats.  South  of  Bagagem,  at  Agua  Suja,  Diamonds 
have  been  found  associated  with  Magnetite,  Ilmenite,  Eutile, 
Garnet  and  Perof  skite,  in  a  ground-mass  consisting  of  blocks 
of  rock  derived  seemingly  from  rocks  which  are  in  situ 
close  by. 

At  Grao  Mogol,  near  the  southern  extremity  of  the  Serra 
Diamantina,  some  hundred  miles  north-north-east  of  the 
town  of  Diamantina,  there  is  a  deposit  of  the  gem  in  a  sand- 
stone; this  sandstone  has  green  Mica  developed  along  its  bed- 
ding planes,  and  contains  the  same  minerals  as  are  associated 
with  the  Diamond  in  the  itacolumite.  This  has  led  to  the 


PRECIOUS  STONES.  117 

belief  that  this  sandstone  is  derived  from  the  weathering  of 
the  older  itacolumite,  and  that  it  is  identical  with  the  sand- 
stone seen  lying  unconformably  on  the  itacolumite  in  the 
Serra  do  Espinha90.  Diamonds  were  first  discovered  at 
Grao  Mogol  in  the  "gurgulho  "  in  1827,  but  were  not  found  in 
the  sandstone  till  1833. 

The  state  of  Bahia,  which  was  formerly  of  small  impor- 
tance as  a  Diamond  producing  region,  has  latterly  been 
more  productive  than  Minas  Geraes.  Diamonds  were 
discovered  in  this  state  in  1755. 

Near  Salobro,  on  the  Bio  Pardo,  nearly  200  miles  south- 
south-west  of  the  town  of  Bahia,  Diamond  occurs  in  clays,  in 
crystals  of  good  quality,  octahedral  in  type.  They  are  sup- 
posed to  be  derived  from  the  crystalline  rocks  around,  but  the 
absence  of  certain  minerals  characteristic  of  these  rocks  in 
Brazil  has  led  to  doubt  being  thrown  on  this  origin. 
Further,  although  the  general  mineral  associates  are  much 
the  same  as  elsewhere  in  Brazil,  there  are  some  remarkable 
exceptions  in  the  presence  here  of  Corundum  and  the 
absence  of  Tourmaline  and  the  oxides  of  titanium. 

West  of  Bahia  about  200  miles,  in  the  Serra  da  Cincora, 
a  rich  deposit  was  discovered  in  1844,  and  since  that  time 
a  large  quantity  of  stones  has  been  obtained  from  the 
locality.  The  Diamond  here  occurs  in  alluvial  and  other 
detrital  deposits,  although  the  hills  around  are  of  granite 
and  gneiss. 

Most  of  the  Carbonado  produced  comes  from  this  locality. 

In  Borneo  deposits  have  been  known  for  a  long  time,  but 
have  never  been  of  any  great  importance  in  comparison 
with  the  foregoing  great  areas  of  production.  One  group,  in 
the  south  of  the  island  near  Bandjermassim,  is  in  gravels 


118  PRECIOUS  STONES. 

lying  on  Tertiary  rocks,  which  in  turn  lie  on  very  old  schists ; 
there  are  also  eruptive  rocks  associated  with  the  Tertiary 
sedimentary  rocks.  The  minerals  here  associated  with  the 
Diamond  are  Quartz,  Corundum,  Magnetite,  Chromite,  and 
some  of  the  noble  metals.  Another  group  in  the  west  of 
Borneo,  near  Pontianak,  is  in  ancient  detritus,  or  in  con- 
glomerates composed  of  rounded  fragments  of  silicious  rocks, 
of  schists,  clay  slates  and  volcanic  rocks.  The  Diamonds 
occur  usually  in  sand  and  alluvial  deposits  resulting  from  a 
further  disintegration  of  these  rocks.  Associated  minerals 
are  Corundum,  Magnetite,  some  Gold,  etc.  The  Diamonds 
themselves,  though  rarely  of  any  great  size,  are  remarkable 
for  their  colour,  especially  the  very  rare  black  Diamonds 
previously  mentioned.  The  varieties  Bort  and  Carbonado 
are  also  present. 

Australia  has  never  produced  any  large  stones,  the 
heaviest  being  one  of  5|  carats  found  in  New  South  Wales, 
the  part  of  the  Commonwealth  which  has  so  far  been  the 
most  productive.  Diamonds  were  first  discovered  in  the 
gold-washings  near  Bathurst  in  1851  on  a  tributary  of  the 
Macquarie  river,  along  which  stream  ancient  detrital 
matter  has  since  afforded  numerous  but  small  stones, 
averaging  about  J  carat.  This  deposit  is  an  old  river 
terrace,  overlaid  by  a  layer  of  basalt.  The  mineral  is 
accompanied  by  Quartz,  varieties  of  Chalcedony,  Cassiterite, 
Topaz,  Corundum,  Brookite,  Garnet,  Zircon,  Magnetite, 
Ilmenite,  Tourmaline,  etc.  Other  deposits  have  been  found 
along  the  upper  part  of  the  Lachlan  river.  In  the  north 
of  New  South  Wales,  not  far  from  the  Queensland  border, 
deposits  occur  on  the  Gwydir  river,  a  tributary  of  the 
Darling.  Here,  too,  the  Diamonds  occur  in  old  alluvium,  and 


PKECIOUS  STONES.  119 

associated  with  much  the  same  group  of  minerals  as  at  the 
locality  near  Bathurst,  but  on  the  Gwydir  the  miners  attach 
special  importance  to  the  presence  of  Tourmaline  as  an 
indicator  of  the  proximity  of  Diamond.  However,  in  1901, 
Mr.  Pittman,  of  the  New  South  Wales  Geological  Survey, 
described  the  occurrence  of  Diamond  in  breccia  filling  an  old 
volcanic  pipe  very  similar  to  the  pipes  of  South  Africa ;  the 
breccia  contained  angular  fragments  of  sedimentary  rocks 
and  acid  volcanic  rocks  as  well  as  of  the  basic  volcanic 
rocks,  basalt  and  eclogite,  and  besides  Diamonds,  Zircon, 
Garnet  and  Diopside  were  seen. 

Diamond  has  been  found  in  all  the  other  other  parts  of 
the  continent ;  that  is,  in  Victoria,  at  Beechworth,  and  other 
localities ;  in  South  Australia,  to  the  south-east  of  Adelaide ; 
in  Western  Australia,  near  Freemantle,  with  Zircon,  Topaz, 
Ilmenite  and  Quartz ;  and  in  Queensland,  on  the  Palmer 
river,  etc.  Diamonds  are  also  said  to  have  been  found  at 
Courina,  in  Tasmania. 

In  1829  the  Diamond  was  discovered  in  Europe,  at  a 
deposit  of  detrital  matter  of  the  Adolfskoi  gold  washings,  not 
far  from  Bissersk,  and  later  at  other  places,  as  Kuschaisk ; 
also  ten  miles  east  of  Katherinenburg  and  other  places ; 
later,  they  have  been  found  in  the  southern  part  of  the  Ural 
mountains.  At  Adolfskoi  the  mineral  was  found  in  a  gold- 
bearing  sand,  associated  with,  besides  Gold,  such  minerals  as 
Magnetite,  Limonite,  Quartz,  and  varieties  of  Chalcedony, 
Platinum  and  Anatase.  The  sand  seems  to  be  derived  from 
matamorphic  rocks  in  the  neighbourhood,  such  as  a  chlorite- 
talc-schist,  with  much  Quartz. 

Lapland  has  provided  a  most  interesting  occurrence  of 
Diamond ;  the  mineral  was  found  on  the  border  of  Kussian 


120  PRECIOUS  STONES. 

Lapland,  close  to  the  Norwegian  frontier,  in  a  valley  near 
Varanger  Fjord.  The  whole  district  consists  of  gneiss 
traversed  by  bands  of  pegmatite,  and  it  was  in  sand  derived 
from  these  rocks  that  the  discovery  was  made.  Of  the 
associated  minerals,  Velain  gives  (the  most  abundant  coming 
first)  Garnet,  Zircon,  Hornblende,  Glaucophane,  Kyanite, 
green  Augite,  Quartz,  Corundum,  Kutile,  Magnetite,  Stauro- 
lite,  Andalusite,  Tourmaline,  Epidote  and  Oligoclase  felspar, 
and  he  believes  the  Diamond  originated  in  the  pegmatite, 
and  at  the  same  time  as  that  rock  was  formed. 

It  is  of  interest  to  note  that  Professor  Heddle  obtained  a 
specimen  of  rock  from  three  miles  north-east  of  Ben  Hope,  in 
Sutherland,  Scotland,  containing  a  "red  Mica,  red  Zircons 
and  either  colourless  Garnets  or  Diamonds,"  and  it  is 
recorded  in  the  "Mineralogy  of  Scotland,"  vol.  ii.,p.  194,  by 
Mr.  A.  Thorns,  that  Dr.  Heddle  was  confident,  in  his  own 
mind,  from  their  optical  properties,  that  these  were 
Diamonds.  The  point  is  of  great  interest,  as  beyond  this 
there  seems  no  record  of  this  mineral  occurring  in  the 
British  Islands.  At  Carratraca,  in  Spain,  Diamond  is 
reported  to  have  been  found  in  a  stream  with  Serpentine. 

In  North  America  Diamonds  have  frequently  been 
found  since  1850,  when  the  first  one  was  discovered  in 
the  alluvial  workings  for  gold  in  California.  Since  this 
time  they  have  been  found  at  intervals  both  in  the 
recent  alluvium  and  also  in  the  ancient  detritus  covered 
by  lava  flows.  The  Californian  localities  include,  in 
Amador  Co.,  Volcano,  where  an  association  with  Garnet  and 
Chalcedony  is  seen  ;  Fiddletown,  with  Gold  and  lead-  and 
copper-ores  ;  in  Butte  Co.,  the  Cherokee  ravine  with  Zircon, 
Chromite,  etc. ;  in  El  Dorado  Co.,  at  Forest  Hill.  In 


PEECIOUS  STONES.  121 

North  Carolina,  at  Brindletown  Creek,  in  Eutherford  Co. ;  at 
Portis  Mines,  in  Franklin  Co.,  with  Gold  in  placer  workings ; 
at  Dysortville,  in  M'Dowell  Co.  Diamonds  have  also  been 
found  sparingly  in  Idaho  and  Oregon,  in  the  west,  and  in 
Georgia  (Hall  Co.).  One  stone  of  23f  carats  was  found  at 
Manchester  (Virginia)  in  1855.  It  is  of  interest  to  note 
that  much  of  the  rock  in  North  Carolina  consists  of  a 
schistose  rock,  and  that  a  flexible  sandstone  similar  to  the 
itacolumite  of  Brazil  is  also  found,  though  it  has  not 
yielded  Diamonds  so  far.  In  Wisconsin  Diamonds  have  been 
found  in  glacial  deposits  with  Quartz,  Garnet,  Ilmenite, 
and  Magnetite.  It  is  pointed  out  by  Professor  Hobbs  that 
the  direction  of  the  ice  movement  shows  that  most  of  this 
glacial  debris  came  from  the  neighbourhood  of  Hudson  Bay. 

In  British  Guiana  Diamonds  have  been  found  in  gold- 
bearing  gravels  at  Omai  Creek  (Harrison).  The  gravels 
seem  to  be  composed  of  weathered  dolerite,  with  Quartz  and 
concretions  of  iron-stone.  On  the  upper  part  of  the 
Mazaruni  river  they  have  been  found  in  gold-bearing 
gravels  associated  with  Spinel,  Tourmaline,  Ilmenite,  Topaz, 
and  Corundum. 

Diamonds  have  also  been  found  in  a  rock  on  the  Sea  of 
Tanjan  in  Malacca,  in  Java,  and  in  Celebes;  also  at  Serra 
Madre,  in  Mexico,  of  the  variety  Carbonado.  King  ("  Precious 
Stones  "),  quotes  Ammian  for  a  locality  known  in  the  fourth 
century  beyond  the  Sea  of  Azov. 

Minute  Diamonds  have  been  found  in  meteorites,  first  in 
one  that  fell  at  Novo-Urei,  in  Eussia,  in  1886 ;  but  as  this 
is  an  extra-terrestrial  origin,  the  reader  must  consult  such 
special  articles  as  Sandberger  ("  Jahrbuch  fur  Mineralogie," 
1889). 


122  PEECIOUS  STONES. 

On  reviewing  the  whole  of  these  occurrences,  it  will  be 
noticed  that  in  the  great  majority  of  cases  the  Diamond  is 
found  in  material  derived  from  the  wasting  of  older  rocks. 
In  some  cases  this  wasting  is  undoubtedly  the  result  of 
ordinary  weathering  by  the  chemical  and  physical  effects 
of  water  in  decomposing  and  mechanically  wearing  away 
the  rocks.  In  other  cases  it  is  more  than  likely  it  was  due 
to  the  influence  of  great  alternations  of  heat  and  cold  in 
the  atmosphere,  principally  aided  by  wind  and  blown  sand. 
The  resulting  detritus  may  occur  as  a  loose  sand  or  gravel, 
or  may  be  re-cemented  into  a  more  or  less  compact  sand- 
stone or  conglomerate.  In  such  cases  we  can  learn  little  of 
the  original  rock  in  which  the  Diamond  was  developed 
except  by  a  study  of  the  associated  minerals.  Where  these 
occur  in  a  fresh  condition  we  may  reasonably  assume  they 
fairly  represent  the  original  constituents  of  the  rock  from 
which  they  came  ;  but  in  all  cases  it  must  be  borne  in 
mind  that  the  Diamond,  by  its  hardness  and  chemical 
stability,  might  have,  so  to  speak,  outlived  all  its  com- 
panions, and  later  have  become  associated  with  a  fresh 
group  of  minerals.  In  such  a  case  we  should  expect  the 
associated  minerals  to  be  different  in  many  instances  ; 
but  a  review  of  the  whole  associates  shows  a  remarkable 
similarity  in  their  kind,  so  we  may  here  tabulate  the  prin- 
cipal associated  minerals  mentioned  in  the  foregoing  pages:— 

Vaal  River. — Garnet,  Ilmenite,  Vaalite  (a  hydrous  ferro- 
magnesian  silicate). 

Kimberley. — Garnet,  Enstatite,  Biotite,  Ilmenite,  Mag- 
netite, Bronzite,  Chrome  Diopside,  Smaragdite,  Tre- 
molite,  Asbestos,  Zircon,  Cyanite,  Sapphire,  Topaz, 
Eutile,  Tourmaline,  Wollastonite,  Serpentine. 


PEECIOUS  STONES.  123 

Mahanadi  River. — Quartz,  Carnelian,  Garnet,  Beryl, 
Topaz. 

Wajra  Karur. — Epidote,  Corundum  (Kuby  and  Sapphire), 
Limonite.  Here  said  to  be  in  situ  in  a  pegmatitic  band  in 
gneiss. 

San  Jodo  da  Chapada. — Quartz,  Haematite  (and  other 
oxides  of  iron),  Eutile,  Anatase,  Tourmaline.  Here  also 
stated  to  bem  situ  in  "veins." 

Agna  Siija. — Magnetite,  Ilmenite,  Eutile,  Garnet,  Perof- 
skite. 

Eio  Jequitinhonha. — Eutile,  Anatase,  Brookite,  Haematite, 
Ilmenite,  Martite,  Quartz,  Garnet,  Zircon,  Cyanite,  Topaz, 
Tourmaline,  Euclase,  Lapis  Lazuli,  Gold,  Limonite,  Iron 
Pyrites,  Monazite,  Sphene,  and  others. 

Salobro. — Many  of  the  associates  of  the  Eio  Jequitinhonha, 
but  without  the  oxides  of  titanium,  and  with  the  addition 
of  Corundum. 

Bandjermassim. — Quartz,  Corundum,  Magnetite,  Chromite, 
Gold. 

Pontianak. — Magnetite,  Corundum,  various  forms  of  silica, 
Gold. 

Upper  Macquarie  River. — Chalcedony,  Cassiterite,  Eutile, 
Quartz,  Ilmenite,  Magnetite,  Brookite,  Zircon,  Topaz, 
Tourmaline,  Corundum,  Garnet. 

Gwydir  River  (alluvial). — Very  similar  to  the  Macquarie 
associates. 

Gwydir  River  (in  breccia). — Zircon,  Garnet,  Diopside. 

Freemantle. — Quartz,  Zircon,  Ilmenite,  Topaz. 

Adolfskoi. — Magnetite,  Quartz,  Chalcedony,  Limonite, 
Anatase,  Gold,  Platinum. 

Varanger  Fjord. — Garnet,  Zircon,  Hornblende,  Glauco- 


124  PEECIOUS  STONES. 

phane,  Cyanite,  green  Augite,  Quartz,  Corundum,  Eutile, 
Magnetite,  Staurolite,  Andalusite,  Tourmaline,  Epidote, 
Oligoclase;  there  is  here  a  strong  presumption  that  the 
Diamond  is  from  the  pegmatite  bands  in  the  gneiss. 

Omai  Creek. — Spinel,  Ilmenite,  Corundum,  Tourmaline, 
Topaz. 

Some  of  the  minerals  yield  us  little  information  from  the 
mere  fact  of  their  occurrence  in  association  with  Diamond. 
Quartz  and  the  other  varieties  of  silica,  for  instance,  occur 
under  such  diverse  conditions  that  we  can  here  draw  no 
conclusions  as  to  the  conditions  under  which  Diamond  was 
developed. 

Many  of  the  others,  however,  are  found  to  occur  under 
very  similar  geological  conditions  in  different  localities. 
Thus  Tourmaline,  Eutile  and  Zircon  are  usually  found  in 
rocks  which  have  been  subjected  to  marked  deformation ; 
they  are  minerals  of  dynamo-metamorphic  origin,  in  other 
words.  Beryl,  too,  often  so  results,  but  it  and  Topaz  are 
sometimes  found  to  have  crystallised  out  late  in  the  con- 
solidation of  granite  masses.  The  oxides  of  iron,  titanium, 
and  chronium  form  an  interesting  group  with  many  inter- 
relations. Many  basic  eruptive  rocks  contain  as  an  original 
constituent  a  slightly  titan  if  erous  oxide  of  iron ;  their 
pyroxenes  too  often  contain  titanium,  replacing  silicon ;  the 
titaniferous  oxide  of  iron  occurring  thus  was  designated 
Iserine  to  distinguish  it  from  ordinary  Magnetite.  "When 
such  a  rock  is  subjected  to  dynamo-metamorphism,  the 
Iserine  splits  up,  true  Ilmenite  resulting  in  some  cases, 
possibly  with  accretion  of  titanium  from  the  pyroxenes.  At 
other  times  a  titaniferous  form  of  Haematite  results,  as 
is  often  seen  in  the  Haematite-schists  such  as  have  been 


PKECIOUS   STONES.  125 

mentioned  as  occurring  in  the  neighbourhood  of  Diamond 
deposits.  Other  titanium  minerals,  as  Eutile  and  Sphene, 
may  also  result  this  way,  though  the  latter  may  be  an 
original  constituent,  or  may  result  from  thermo-metamor- 
phism.  Should  the  pyroxenes  contain  chromium,  Chromite 
may  be  formed  ;  more  often  this  is  the  result  of  hydro- 
rnetamorphism  in  conjunction  with  the  formation  of  Ser- 
pentine. It  is  almost  impossible  to  draw  any  sharp  line 
between  these  various  forms  of  metamorphism ;  probably 
the  action  is  always  complex.  Of  the  minerals  found  in 
association  with  Diamond,  many  usually  result  from  thermo- 
metamorphism  or  from  complex  changes  in  which  it  bears  an 
important  part.  Thus  many  of  the  Garnets,  Tremolite, 
Wollastonite,  Sphene,  Spinel,  may  be  found  where  a  rock 
containing  much  calcium  is  acted  on ;  in  argillaceous  rocks 
Cyanite,  Andalusite,  Staurolite,  and  some  of  the  Garnets  may 
result.  The  action  of  water  under  great  pressure  and 
probably  at  a  considerable  temperature  in  most  cases, 
which  brings  about  the  formation  of  these  minerals  is  at 
the  same  time  changing  the  whole  rock  so  that  a  pegmatite 
or  gneiss  may  result  where  the  pressure  is  very  great  and 
is  only  relieved  slowly,  whereas  if  the  pressure  is  somewhat 
less  and  relief  takes  place  suddenly  an  eruptive  rock  may 
result  (J.  G.  Goodchild,  H.  M.  Geol.  Survey.,  "Proc.  Koyal 
Phys.  Soc."  Vol.  XIV.).  The  theory  that  such  rocks  are  the 
result  of  a  regeneration  of  this  kind  seems  in  accordance 
with  the  facts  as  observed  in  the  field ;  if  so,  many  of  the 
difficulties  surrounding  the  apparently  diverse  origin  of 
Diamond  become  much  less.  In  the  two  most  reliable 
instances  of  occurrence  in  situ  recorded  until  lately — namely, 
at  Wajra  Karur  and  in  Lapland — both  observers  referred 


126  PKECIOUS  STONES. 

the  original  site  to  the  pegmatite  bands  in  those  localities. 
In  the  Lapland  instance  the  gem  was  not  actually  in  situ, 
but  the  surrounding  rocks  were  of  so  similar  an  origin  as  to 
make  the  presumption  strong.  Moreover,  the  pegmatite 
bands  and  the  gneiss  would  appear  to  be  but  an  earlier  and 
later  stage  of  the  same  metamorphosis.  Gorceix  concluded 
the  San  Joao  Diamonds  had  also  originated  in  pegmatite 
"  veins."  The  fact  that  in  these  bands  Quartz,  Anatase  and 
Haematite,  seem  to  have  been  simultaneously  formed  with 
the  Diamond,  recalls  the  changes  described  above  concern- 
ing these  oxides.  Eodgers  ("  Geology  of  Cape  Colony  ")  points 
out  that  although  the  materials  filling  the  pipes  of  South 
Africa  differ  so,  yet  there  are  gradations  from  one  type  to 
another;  and  Prof.  Bonney  (Geol.  Mag.,  1899,  p.  309) 
records  the  presence  of  Diamond  in  eclogite  (an  ultra-basic 
rock  without  Olivine)  from  Newland's  mine  in  Griqualand 
West.  Kodgers  concluded  that  the  Kimberley  Diamonds 
probably  originated  in  a  deep-seated  ultra-basic  rock- 
magma,  explosions  proceeding  from  this  or  a  lower  horizon 
having  filled  the  pipes  with  brecciated  material  containing 
a  large  proportion  of  ferro-magnesian  silicates ;  subsequent 
hydration  would  convert  the  material  into  a  serpentinous 
mass  such  as  is  there  seen. 

Great  stress  has  been  laid  on  the  association  with  Olivine, 
but  there  are  many  occurrences  without  this  associate,  and 
in  any  case,  if  Diamond  originates  by  this  action  of  heated 
waters  the  same  action  could  affect,  and  apparently  does 
affect,  rocks  containing  no  Olivine.  Although  it  has  been 
allowed  that  the  pegmatite  bands  might  represent  the  solidi- 
fication of  fused  silicates  saturated  with  water,  the  full 
importance  of  the  water  does  not  seem  to  have  been  given 


PKEOIOUS  STONES.  127 

due  prominence  to,  although  Daubree  in  1876  stated  that 
highly  heated  water  would,  even  in  a  few  days  transform 
three  times  its  weight  of  amorphous  silicates  into  Quartz 
and  crystallised  silicates.  This  in  man's  laboratory;  in 
Nature's  laboratory,  with  great  time  and  great  stores  of 
energy,  how  much  greater  changes  can  conceivably  be 
wrought !  The  formation  of  gneiss  has  been  assumed  to 
be  independent  of  the  action  of  water ;  such  is  probably 
not  the  case,  water  being  on  the  contrary  an  essential 
factor. 

CHEMICAL  COMPOSITION. 

Diamond  consists  of  pure  carbon,  an  element  which  also 
occurs  in  Nature  in  an  allotropic  form,  Graphite.  As  might 
be  expected,  the  composition  of  this  remarkable  mineral 
very  long  ago  was  the  subject  of  speculation.  Boetius  de 
Boot,  in  1609,  stated  his  supposition  that  it  was  a  combus- 
tible substance,  and  in  1673  Robert  Boyle  discovered  that 
under  the  influence  of  a  high  temperature  it  was  "dissipated 
in  acrid  vapours."  About  twenty  years  later  two  Academi- 
cians of  Florence  experimented  in  the  presence  of  the  Duke 
of  Tuscany  and  confirmed  Boyle's  observation,  and  a  hundred 
years  after  that  again,  Macquer  and  Bergman  continued  the 
experiments  with  the  same  result.  In  1772  Lavoisier 
showed  that  it  was  only  when  heated  in  contact  with  air  or 
oxygen  that  it  so  disappeared,  and  he  further  proved  that 
the  product  of  its  combustion  caused  a  precipitate  in  lime 
water  which  effervesced  on  treatment  with  an  acid,  as  did 
also  the  product  of  the  combustion  of  carbon.  Then,  in  1797, 
Tennant  showed  that  the  amount  of  carbon  dioxide  formed 
from  a  given  weight  of  Diamond  was  the  same  as  that 


128  PEECIOUS  STONES. 

formed  from  an  equal  weight  of  carbon,  and  hence  established 
the  identity. 

According  to  Moissan,  Diamond  unites  with  oxygen  when 
a  temperature  of  620°  to  840°  C.  is  reached,  and  Lavoisier 
gives  the  temperature  of  ignition  in  air  as  916°  C.  In 
oxygen  it  burns  with  a  pale  blue  flame,  and  continues 
burning  after  the  source  of  heat  is  withdrawn.  It  is 
insoluble  in  all  the  ordinary  solvents  (see  Sir  W.  Crookes' 
account  of  Moissan' s  experiments  under  Artificial  Pro- 
duction). 

When  heated  in  the  electric  arc  away  from  oxygen,  a 
slow  conversion  to  Graphite  takes  place,  and  Despretz,  by  the 
use  of  an  electric  spark  from  some  five  hundred  Bunsen 
cells,  detected  some  beads  as  though  fusion  took  place 
when  the  heating  was  very  prolonged.  Only  specimens 
containing  impurities  leave  any  ash  on  ignition.  From  the 
variety  Carbonado,  Rivot  found  the  ash  varied  from  0'24  to 
2*03  per  cent. ;  the  ash  consists  chiefly  of  the  oxides  of  iron, 
silicon  and  calcium.  Inclusions  of  other  minute  Diamonds 
have  been  observed,  and  also  of  Haematite,  and  possibly  of 
Eutile  or  Ilmenite.  As  with  many  other  minerals,  enclosures 
of  liquid  carbon  dioxide  are  sometimes  seen  ;  in  some  cases 
these  are  so  numerous  and  so  minute  as  to  give  the  crystal 
a  clouded  appearance. 

METHODS  OF  MINING. 

The  means  taken  to  separate  Diamond  from  its  surround- 
ings vary  with  the  nature  of  the  deposit,  but  may  be 
generally  classified  as  to  whether  the  deposit  is  a  river  or 
alluvial  one,  or  one  in  more  solid  material  as  at  Kimberley. 
In  river  workings  the  usual  method  adopted  is  to  divert  part 


PRECIOUS  STONES.  129 

of  the  stream  by  means  of  a  dam,  or  by  cutting  a  flume,  the 
bed  of  the  river  so  exposed  being  then  cleared  of  all  its 
gravel,  which  is  carefully  saved.  The  stream  is  diverted 
when  the  water  is  as  low  as  possible,  and  the  gravel  put 
aside  till  the  rainy  weather  when  work  in  the  river  is  no 
longer  feasible;  then  the  gravel  is  placed  on  a  sloping  table 
some  5  feet  by  2  feet,  with  a  pit  at  the  lower  end,  in 
which  the  workers  stand.  About  a  barrowful  of  material  is 
treated  at  a  time ;  the  gravel  is  placed  at  the  upper  end  of 
the  table  and  water  thrown  over  it  to  wash  away  the  lighter 
minerals ;  the  residue  is  hand-washed  in  bowls  in  much  the 
same  way  as  in  ''panning"  for  gold,  and  the  Diamonds 
picked  out  by  hand.  In  searching  the  river  bed  particular 
attention  is  paid  to  the  pot  holes,  as  they  often  give  a  rich 
yield.  Thus  Dr.  Cliffe  records  that  one  such  hole  in  Brazil 
yielded  10  Ibs.  of  Diamonds  and  28  Ibs.  of  Gold  when 
discovered  in  1847. 

In  the  Kimberley  deposits  the  original  method  of  working 
was  somewhat  similar,  but  gradually  as  the  claims  were 
worked  further  and  it  was  found  that  the  deposit  extended 
to  greater  depths,  other  methods  had  perforce  to  be  adopted. 
Different  claims  were  worked  with  varying  degrees  of  enthu- 
siasm, and  soon  the  workings  presented  a  wonderful  assort- 
ment of  rectangular  pillars,  with  corresponding  depressions 
here  and  there  where  some  miners  had  pushed  on  the  work 
at  a  greater  rate.  The  material  was  hauled  up  on  wire 
ropes,  one  for  each  claim,  and  the  maze  of  wires  added  to 
the  extraordinary  appearance.  Tracks  left  between  groups 
of  claims  to  act  as  roads  began  to  give  way  and  several 
large  slips  occurred.  Soon  one  gigantic  pit  resulted,  and 
to  add  to  the  difficulties  of  the  miners  still  more,  water 

P.S.  K 


130  PEECIOUS  STONES. 

began  to  give  trouble  in  the  wet  weather,  its  absence  in  the 
dry  season  being  equally  troublesome.  These  difficulties 
were  overcome  by  the  gradual  combination  of  the  workers, 
and  finally  the  whole  group  passed  into  the  hands  of  the 
De  Beers  Company,  whose  great  capital  has  enabled  work 
to  be  carried  on  in  a  scientific  way. 

At  present  in  the  Kimberley  mines  the  blue  ground  is 
worked  by  shafts  sunk  in  the  solid  Karoo  beds,  from  which 
levels  run  out  to  cut  the  pipe.  The  blue  ground  so  obtained 
is  laid  out  on  depositing  floors  of  large  area ;  on  these,  the 
blue  ground  spread  out  to  a  depth  of  30  inches  or  so, 
crumbles  down  under  the  influence  of  atmospheric  changes, 
the  process  requiring  from  a  few  months  to  two  years,  the 
resistance  of  the  material  varying  in  different  mines,  and 
in  different  parts  of  the  same  mine  even.  Any  material 
which  does  not  soften  under  this  treatment  is  disintegrated 
mechanically.  The  broken  down  material  is  next  washed 
and  concentrated  in  machines  somewhat  like  the  "buddies" 
and  "  jiggers "  of  metalliferous  mines,  advantage  being 
taken  of  the  higher  specific  gravity  of  the  Diamond  to 
separate  it  from  the  lighter  minerals,  though  several  of  its 
associated  minerals  being  of  nearly  as  great,  or  in  some 
cases  greater,  density,  remain  with  it ;  from  such  the 
Diamond  was  till  recently  separated  by  hand,  the  washed 
gravel  being  fed  on  to  a  long  shallow  trough  lined  with  zinc, 
and  having  a  slight  slope.  The  gravel  reaching  the  table 
at  the  higher  end  along  with  a  stream  of  water  was  moved 
along  by  the  sorters  standing  at  the  side  by  means  of  small 
flat  pieces  of  thin  metal,  and  any  gems  picked  out  and 
placed  in  small  dishes,  according  to  their  kind  and  quality. 
Great  dexterity  was  shown  in  this  sorting  and  a  remarkable 


PRECIOUS  STONES.  131 

keenness  of  sight,  any  doubtful  mineral  being  adroitly 
tapped  with  the  metal,  apparently  with  a  view  to  determin- 
ing its  nature  by  its  "  feel."  Now,  however,  the  gravel  is 
passed  over  a  vibrating  table  with  a  stepped  outline,  the 
steps  being  covered  with  a  thick  layer  of  grease,  to  which 
the  Diamonds  adhere  (Claremont). 

APPLICATIONS. 

Besides  its  use  in  ornament  there  are  certain  technical 
purposes  for  which  Diamond  is  used.  Perhaps  the  most 
familiar  use  is  in  cutting  glass,  and  it  is  a  common  belief 
that  any  bit  of  Diamond  will  do  for  this  purpose ;  but  a  glazier 
would  soon  tell  one  this  is  not  the  case.  It  is  found  that 
the  best  form  for  this  purpose  is  a  natural  crystal  having 
markedly  curved  faces,  meeting  in  a  not  too  obtuse  edge. 
When  such  a  crystal  is  mounted  in  its  holder  and  lightly 
applied  to  the  glass  with  the  faces  bounding  this  edge 
making  equal  angles  with  the  glass,  and  the  glass  itself 
making  a  tangent  to  the  curved  edge,  a  clear  scratch  will 
result  almost  like  a  cut,  though  only  about  2W  mcn  in 
depth.  Even  with  a  suitable  Diamond  it  requires  consider- 
able skill  to  cut  glass  properly,  and  different  cutters  have 
to  be  used  for  different  kinds  of  glass.  In  mounting  the 
crystal,  attention  should  be  given  to  the  varying  hardness 
in  different  directions,  so  that  if  a  suitable  edge  presents  it 
may  be  utilised.  Wollaston  ground  other  gem  stones  into 
a  form  similar  to  that  between  two  curved  faces  of  Diamond 
and  found  them  satisfactory,  though  not  so  durable  as  the 
usual  cutter. 

Diamond  is  also  largely  used  in  the  manufacture  of  rock 
drills.  For  this  purpose  the  varieties  Bort  and  Carbonado 

K  2 


132  PRECIOUS  STONES. 

are  preferred  on  account  of  their  smaller  liability  to 
damage,  cleavage  being  less  prominent  than  in  the  crystal- 
lised variety,  or  absent.  Some  specimens  of  Bort  and 
Carbonado  also  show  a  hardness  superior  to  the  gem  variety. 
In  use,  circular  rings  of  steel,  called  "  crowns,"  are  drilled 
on  the  flat  surface  with  small  holes,  in  each  of  which  a 
small  piece  of  Bort  is  set,  usually  by  drawing  the  mild 
steel  partly  over  the  stone ;  so  armed,  the  crown  makes  a 
rapid  rock-cutting  tool  for  boring  artesian  wells  or  making 
prospecting  bores.  An  advantage  of  this  method  is  that 
solid  cores  are  brought  up  and  can  be  retained  for  reference 
as  to  the  rocks  passed  through.  The  use  of  Diamond  as  an 
abrading  agent  has  already  been  referred  to  under  the 
cutting  of  gems ;  it  may  be  noted  that  the  dust  produced 
in  the  bruting  of  Diamonds  is  more  efficient  on  account 
probably  of  the  flakes  being  taken  off  with  a  definite 
relation  to  the  directions  of  greatest  hardness.  Diamond 
powder  is  used  now  not  only  in  the  grinding  and  polishing 
of  Diamond,  but  also,  on  account  of  the  resulting  increased 
speed  of  work,  in  the  grinding  and  slitting  of  such  gems  as 
Ruby,  Sapphire,  Chrysoberyl,  Topaz,  etc. 

Diamond  has  been  used  for  making  small  drills  to  pierce 
the  other  gem  stones  for  ornamental  purposes,  and  for 
wire-drawing  dies,  and  for  drilling  the  jewelled  bearings 
for  watches ;  also  for  use  as  a  small  milling  cutter  with 
which  to  engrave  gems  and  cut  seals  and  cameos. 

Dr.  Goring  suggested  its  use  for  microscope  lenses,  and 
these  lenses  were  actually  made  by  Pritchard  ;  but  a  diffi- 
culty arose  from  the  specimens  used  showing  optical 
anomalies  due  to  internal  strain,  also  from  the  great 
labour  and  cost  of  manufacture. 


PKECIOUS  STONES.  133 

It  is  used  to  provide  a  cutting  edge  for  lathe  tools 
intended  for  the  working  of  very  hard  steel,  and  Max  Bauer 
instances  its  use  in  tools  for  boring  cannon  at  Krupp's 
works  at  Essen. 

Of  its  more  frequent  use  for  personal  adornment  little 
more  need  be  said.  From  the  time  it  was  first  known 
Diamond  has  held  its  place  with  a  uniformity  more  marked 
than  any  other  precious  stone.  An  exception  is  given  by 
King,  who  states  that  the  Persians  only  allowed  it  to  rank 
after  Pearl,  Euby,  Emerald,  and  Chrysolite. 

In  the  earliest  times  the  gem  seems  to  have  been  used 
largely  as  a  spell  against  plagues,  and  the  more  alarming 
manifestations  of  Nature's  activity;  in  mediaeval  times, 
chiefly  as  signs  of  magnificence  and  wealth.  Thus  the 
robes  and  crowns  of  kings  were  adorned  with  them,  and  it 
was  not  till  the  middle  of  the  fifteenth  century  that  it 
became  much  in  vogue  for  personal  adornment  by  women, 
at  which  time  it  was  introduced  by  the  ladies  of  the  French 
court. 

Diamond  as  a  rule  requires  little  preparation  before 
cutting  begins.  Should  the  stone  show  surface  films  these 
are  usually  easily  removed  by  treatment  with  "aqua-regia" 
(a  mixture  of  hydrochloric  and  nitric  acids).  Any  imper- 
fections are  removed  as  far  as  possible  by  cleaving,  and  the 
stone  at  the  same  time  brought  to  the  octahedral  form, 
ready  for  grinding,  if  it  is  to  be  cut  as  a  brilliant.  By  far 
the  greatest  number  of  stones  are  cut  after  this  pattern 
now.  So  much  has  Diamond  come  to  be  associated  with 
the  brilliant  cut  that  the  term  "  brilliant "  is  often 
erroneously  used  as  synonymous  with  Diamond.  Even 
very  small  stories  can  be  cut  as  brilliants  by  the  Dutch 


134  PBECIOUS  STONES. 

cutters,  though  as  a  rule  the  full  number  of  facets  are  not 
worked  on  them.  Specimens  which  are  too  thin  to  be  cut 
as  brilliants  are  rose-cut,  and  very  thin  cleavage  slices  are 
often  polished  on  the  two  parallel  surfaces  and  used  as  a 
cover  for  miniatures. 

Brilliants  are  almost  always  mounted  now  in  an  open 
setting,  or  set  "  a  jour  ";  that  is,  they  are  held  by  a  series 
of  metallic  prongs,  projecting  towards  the  girdle.  These 
prongs  are  notched  at  the  end,  and  one  part  goes  above 
the  girdle  and  the  other  below,  thus  firmly  holding  the 
stone  and  leaving  the  culasse  exposed.  Previously  Diamonds 
were  always  set  in  a  closed  setting,  completely  covering  the 
culasse ;  and  this  portion  of  the  stone  was  covered  with  a 
"  tincture,"  a  varnish  made  of  mastic,  coloured  with 
ivory  black,  which  was  supposed  to  add  to  the  beauty  of  the 
gem.  A  stone  showing  darker  patches  is  sometimes  mounted 
in  a  closed  setting,  and  this  varnish  applied  so  as  to  come 
below  the  lighter  portion ;  thus  the  stone  will  seem  of 
more  uniform  appearance.  This  is  known  as  "  mounting 
on  moor." 

Kose-cut  stones  are  always  mounted  in  a  closed  setting. 

VALUE. 

Of  the  value  of  Diamonds  it  is  difficult  to  speak  with  any 
precision,  as  so  much  depends  on  the  quality  of  the  stones, 
and  in  the  case  of  large  stones,  which  very  few  people  could 
afford  to  buy,  so  much  depends  on  whether  any  such  people 
wish  to  buy  at  that  time.  The  old  rule  of  Tavernier  to  find 
the  value  of  a  given  Diamond,  cut  as  a  brilliant  and  of  the 
finest  quality,  was  to  square  its  weight  in  carats,  and 
multiply  by  eight.  Hence  a  stone  of  two  carats  was  worth 


PEECIOUS  STONES.  135 

2  X  2  X  8,  or  £32  while  one  of  three  carats  would  be 

3  X  3  X  8,  or  £72 ;   this  however  gave  too  high  a  value 
even  at  the  time  it  was  introduced  ;  in  1869  when  a  rough 
Diamond    of    one   carat   was   worth    about    £5,    Schrauf 
suggested  another  rule  by  which  the  value  in  pounds  would 
be  found  by  dividing  the  weight  in   carats  by  two,  and 
multiplying  this  dividend  by  the  weight  in  carats  plus  two, 
and  by  the  value  of  a  stone  of  one  carat.     Thus,  if  a  stone 
of  one  carat  were  worth  £12  cut,  a  stone  of  the  same  quality, 
but  weighing  two  carats,  would  be  worth  f  (2  4-  2)  X  £12, 
or  £48.     A  rose-cut  stone  of  the   "first  water"  is  worth 
about  four-fifths  as  much  as  a  brilliant-cut  one  of  the  same 
quality.     First  water  stones  are  those  which  are  perfect ; 
those  of  the  "second  water"   are  such  as  only  show  slight 
imperfection — either  flawless,  but  tinged  with    colour,  or 
colourless,  but  with  slight  flaws.     "  Third  water  "  stones 
show  more  marked  flaws,  or  departure  from  the  colourless 
ideal.     "  Fancy  stones  "  are  those  of  marked  and  beautiful 
colour,  and  such  cannot  be  valued  by  any  rule.     A  brilliant 
of  the  second  water  is  worth  about  two-thirds  as  much  as 
one  of  the  first  water,  but  a  rose-cut  stone  of  the  second 
water  does  not  differ  so  much  from  one  of  the  first  water. 
With  the  increased  production  these  values  are  not  very 
reliable,  and  smaller  stones  of  all  but  the  first  water  only 
increase  in  value  in  direct  proportion  to  their  weight.     A 
first  water  stone  of  one  carat  cut  as  a  brilliant  may  now 
bring  £15  to  £25. 

COUNTERFEITING  AND  KECOGNITION. 

The  Diamond  may  be  imitated  by  other  colourless  gems,  as 
Topaz,  Corundum,  Spinel,  Quartz,  Phenakite,  or  Tourmaline, 


136  PBECIOUS   STONES. 

or  by  Zircon  whose  colour  has  been  discharged  by  heating. 
Diamond  differs  from  all  these  by  its  greater  dispersive 
power  and  consequent  greater  "  fire."  Its  lustre  is  much 
higher  than  that  of  any  of  the  other  minerals  mentioned, 
except  Zircon,  which  may  approach  it.  Probably  the  most 
ready  test  of  all  is  that  of  hardness,  and  for  this  purpose 
carborundum  is  very  well  suited,  for  should  the  stone  be 
genuine,  it  will  not  be  scratched,  but  should  an  inferior 
stone  have  been  fraudulently  substituted  the  carborundum 
will  scratch  it,  even  if  it  be  of  hardness  equal  to  9  of  Mohs' 
scale  (Corundum).  It  should  be  noticed  that  both  the  crown 
and  the  culasse  should  be  tested  (see  "  Doublets  "  under 
Artificial  Production).  In  considering  the  purchase  of  a 
valuable  stone  it  should  always  be  seen  unmounted.  Its 
single  refraction  would  show  it  to  be  a  cubic  mineral,  while 
of  the  above  imitations  only  Spinel  agrees  in  this  respect, 
and  Spinel  is  readily  distinguished  by  its  inferior  hardness. 
The  specific  gravity  of  Diamond  also  is  of  some  help,  though 
Spinel,  Topaz  and  possibly  Tourmaline  might  be  confused 
with  it  in  this  respect. 

Glass  imitations  have  almost  as  high  a  dispersive  power, 
if  good,  but  their  inferior  hardness  is  very  marked,  and  good 
glass  imitations  are  usually  sold  as  such. 

The  great  test  in  De  Boot's  time  was  that  of  applying  the 
"tincture" — the  varnish  mentioned  above;  a  Diamond 
became  more  brilliant,  but  an  imitation  became  less 
brilliant  when  the  "tincture"  was  applied  to  the  under 
surface. 

FAMOUS  DIAMONDS. 

A  Diamond  whose  history  is  as  old  as  any,  perhaps,  was 
the  one  worn  by  Charles  the  Bold  in  his  pendant,  It  was 


PEECIOUS  STONES.  137 

not  very  large  in  comparison  with  many  stones  now  known, 
measuring  some  f  inch  on  the  edges  of  the  girdle,  and  it 
would  probably  weigh  about  30  carats ;  but  it  is  of  great 
interest  as  being  the  first  stone  cut  by  De  Berquem.  Some 
of  the  traditions  concerning  it  have  been  given  when  dealing 
with  the  history  of  cutting. 

The  Sancy,  with  which  Charles  the  Bold's  Diamond  has 
often  been  confused,  is  a  stone  of  53f  carats.  It  is  said  to 
have  belonged  to  a  French  nobleman  called  De  Sancy,  from 
whom  it  passed  to  either  our  Queen  Elizabeth  or  Henrietta 
Maria ;  it  finally  passed  back  to  France  to  the  possession  of 
Louis  XIV.,  but  was  stolen  at  the  time  of  the  Eevolution 
and  not  recovered.  After  being  amongst  the  Spanish 
regalia,  it  passed  in  1828  to  Prince  Demidoff,  and  it  is  now 
owned  by  the  Maharaja  of  Patiala.  It  is  cut  as  a  double 
rosette. 

Three  other  stones  whose  history  is  obscure  and  inter- 
woven are  the  Great  Mogul,  the  Koh-i-noor,  and  the  Orloff. 
The  Mogul  was  seen  by  Tavernier  in  1665,  during  his  visit 
to  India,  amongst  the  jewels  of  Aurungzebe,  when  it  was 
weighed  and  drawn  by  him.  It  is  supposed  to  have  been 
found  in  the  mines  of  Kollur,  and  to  have  weighed  560  to 
787J  carats  in  the  rough ;  it  was  cut  into  a  high-crowned 
rose  by  Borghis  of  Venice,  the  finished  weight  being  280 
carats.  King  records  that  Aurungzebe  was  so  enraged  at 
the  diminution  in  size,  that  instead  of  paying  his  jeweller 
for  cutting  the  stone,  he  fined  him  10,000  rupees.  What 
came  of  the  Great  Mogul  is  not  definitely  known,  but  it  has 
been  supposed  that  it  was  divided  into  three  stones,  of 
which  the  Koh-i-noor  and  the  Orloff  are  two.  It  has  also 
been  stated  that  the  Mogul  was  taken  by  Nadir  Shah  at 


138  PKECIOUS  STONES. 

Delhi,  and  it  may  be  still  amongst  the  Persian  jewels.  It 
is  noteworthy  that  De  Boot  mentions  a  stone  of  187J  carats 
as  an  Indian  one,  of  which  there  is  no  other  record  unless 
it  is  identical  with  the  Koh-i-noor,  which  weighed  186^ 
carats  before  it  was  recut.  In  this  case  it  seems  likely  that 
the  Great  Mogul  was  not  divided. 

The  Koh-i-noor  also  passed  from  the  Mogul  Empire  at 
the  conquest  of  it  by  the  Persians  in  1739.  Later  it  was 
in  the  possession  of  Eunjeet  Sing,  who  wore  it,  alone,  on 
his  arm ;  at  times  it  was  used  to  decorate  the  trappings  of 
his  horses.  On  the  annexation  of  the  Punjab  it  passed  to 
the  East  India  Company,  by  whom  it  was  presented  to 
Queen  Victoria  in  1850.  It  was  exhibited  at  the  Great 
Exhibition  and  recut  in  London  by  Dutch  cutters  in  1852, 
the  work  costing  some  £8,000.  In  its  recut  state  its  weight 
is  106  carats. 

The  Orloff  Diamond  has  also  a  mysterious  past;  it  is 
reported  to  have  formed  an  eye  for  an  idol  in  a  Brahmin 
temple  at  Seringham,  to  have  been  stolen  by  a  French 
soldier,  and  passed  by  the  hands  of  an  English  sea  captain 
to  Amsterdam,  where  it  was  bought  for  Catherine  II.  of 
Eussia  by  Prince  Orloff.  It  is  now  set  on  the  top  of  the 
Imperial  sceptre  of  Eussia.  Its  weight  is  195  carats. 

Another  famous  Diamond  from  the  Kollur  Mines  was 
the  blue  stone  lately  belonging  to  Mr.  H.  P.  Hope. 
It  also  was  exhibited  at  the  1851  Exhibition,  set,  with  a 
border  of  twenty  brilliant-cut  Diamonds  of  the  first  water, 
as  a  medallion.  It  is  of  a  rich  Sapphire  blue  with  great 
fire  and  brilliancy  ;  its  weight  is  44J  carats. 

The  Eegent,  or  Pitt  Diamond,  is  usually  considered  one  of 
the  finest  am}  most  perfectly  cut  stones  in  existence,  It  was 


PEECIOUS  STONES.  139 

found  at  the  Partial  Mines  in  India  in  1701,  and  was 
bought  by  Governor  Pitt  for  £20,400  ;  later  it  was  bought 
by  the  French  Eegent  for  £80,000,  and  was  cut  in  London 
at  a  cost  of  £5,000.  It  was  stolen  with  the  Sancy  Diamond 
in  1792,  but  recovered,  and  still  remains  the  property  of  the 
French  nation.  In  the  rough  it  weighed  410  carats,  when 
cut  it  was  137  carats  ;  in  form  it  is  a  typical  brilliant 
(Fig.  8). 

Of  the  few  engraved  Diamonds  three  may  be  mentioned. 
The  "Shah"  is  an  elongated  stone  chiefly  bounded  by 
cleavage  planes ;  on  it  were  engraved  the  names  of  three 
Persian  kings ;  it  is  amongst  the  Kussian  jewels.  The 
Akbar  Shah  was  engraved  with  an  Arabic  inscription ;  it  is 
now  owned  by  the  Gaikwar  of  Baroda.  Queen  Victoria  had 
in  her  collection  of  engraved  gems  a  large  yellow  Diamond 
engraved  with  the  Prince  of  Wales'  crest ;  it  belonged  to 
Charles  II.  when  Prince  of  Wales. 

The  "  Dresden  Green"  Diamond  and  the  "Kussian  Bed" 
have  already  been  referred  to. 

The  "  Star  of  South  Africa  "  was  found  in  1869  in  river 
diggings,  and  passed  from  a  Kaffir  to  Schalk  van  Niekerk. 
Its  weight  in  the  rough  was  83J  carats,  and  when  cut  as  a 
brilliant  46J. 

The  "Victoria"  is  also  a  South  African  stone ;  its  weight, 
rough,  was  457J  carats.  In  1893  a  stone  of  971f  carats 
was  found  at  the  Jagersfontein  Mine.  From  it  a  perfect 
brilliant  of  239  carats  was  cut,  and  this  is  known  as  the 
"  Excelsior,"  or  "  Jubilee  "  Diamond.  A  stone  of  655  carats 
was  found  at  the  same  mine  in  1895. 

But  far  exceeding  all  previous  South  African  Diamonds, 
and  also  all  previously  heard  of  specimens,  is  the  stone 


140  PRECIOUS  STONES. 

found  at  the  New  Premier  Mine  near  Pretoria  on  January 
25th,  1905.  It  was  found  in  the  yellow  ground,  about 
18  feet  below  the  surface.  It  was  named  the  "  Cullinan," 
after  the  chairman  of  the  Premier  Company.  Its 
weight  is  3,024f  carats,  and  in  size  it  may  be  roughly 
compared  with  a  man's  tightly-clenched  fist,  its  longest 
measurement  being  rather  over  4  inches.  A  detailed 
account  of  it  will  be  found  in  the  paper  by  Dr.  Hatch  and 
Mr.  G.  Corstorphine  ("  Trans.  Geological  Soc.  of  S.  Africa," 
Vol.  VIII.,  p.  26).  A  great  satisfaction  will  doubtless  be 
felt  by  all  lovers  of  precious  stones  at  the  decision  of  the 
Transvaal  Colony  to  present  this  famous  Diamond  to 
His  Majesty  the  King,  thus  ensuring  to  the  Empire  its 
possession  for  all  time. 

The  largest  Brazilian  Diamond  is  the  "  Star  of  the  South," 
found  near  Bagagem  in  1858.  It  weighed  254J  carats  when 
rough  and  was  cut  into  a  brilliant  of  125  carats. 

A  great  mass  of  information  concerning  Diamond  will  be 
found  in  the  work  by  M.  E.  Boutan  ("Le  Diamant,"  Paris, 
1886). 


CHAPTEK  VII. 

175.    FLUOR    SPAR. — OPAL.' 

THIS  mineral,  although  it  occurs  in  such  a  variety  of 
beautiful  colours,  is  but  rarely  used  as  a  precious  stone. 
This  is  largely  due  to  its  comparative  softness,  but  also,  in 
all  probability,  to  its  abundance ;  and  when  it  is  used  it  is 
too  frequently  with  the  prefix  "false" — "false  Topaz," 
"  false  Emerald,"  for  instance.  This  is  jarring  to  the  lover 
of  minerals,  for  why  not  accept  its  undoubted  beauty  for 
what  it  is  worth,  and  under  its  own  simple  name  ? 

The  range  of  colour  it  shows  is  as  varied  as  any  mineral 
known,  but  the  shades  of  most  importance  from  the  present 
point  of  view  are  those  that  are  pure  and  well  marked. 
Thus  it  is  found  of  a  rich  blue,  bright  green,  rose-red, 
sometimes  almost  ruby-red,  a  rich  honey-yellow,  lilac, 
amethystine-violet  and  many  other  colours. 

Its  lustre  is  usually  vitreous,  but  may  be  almost 
adamantine ;  it  varies  from  perfectly  transparent  to 
subtranslucent. 

Eefraction  is  normally  single  with  a  refractive  index  ny 
1-43,  but  it  often  shows  anomalous  double  refraction,  which 
persists  even  at  a  dull  red  heat. 

When  heated  gently  it  shows  marked  phosphorescence, 
the  colour  of  the  light  emitted  varying  and  having  no  rela- 
tion to  the  colour  in  daylight.  Some  varieties  give  a  distinct 
green  light. 


142  PRECIOUS   STONES. 

Fluorescence  is  strongly  marked  in  some  specimens. 
Other  effects  of  heat  are  seen,  one  of  the  most  striking- 
being  the  way  it  decrepitates  if  heated  suddenly,  due,  it  is 
supposed,  to  minute  cavities  within  the  mineral,  containing 
in  many  cases  liquids.  A  change  of  colour  may  also  occur 
on  heating,  the  blue  and  violet  shades  changing  to  purple. 
By  itself  it  is  not  readily  fusible,  but  when  mixed  with  some 
other  substances  it  easily  fuses  to  a  slag  and  on  this  account 
is  largely  used  as  a  flux ;  hence,  possibly,  the  name. 

On  heating,  a  difference  of  electrical  potential  is  induced 
between  the  cube  faces  and  angles  of  the  cube ;  this  also 
occurs  when  light  falls  on  the  crystal. 

The  specific  gravity  varies  between  3*01  and  3'19. 

Crystals  show  a  conchoidal  fracture  and  a  very  perfectly 
developed  octahedral  cleavage.  On  account  of  this  cleavage, 
Fluor  Spar  may  be  used  to  practice  on  to  gain  skill  in  the 
cleavage  of  Diamonds,  and  Tennant  has  used  the  mineral 
to  make  models  of  well-known  Diamonds  with  a  view  to 
ascertaining  the  probability  of  the  Great  Mogul  Diamond 
having  been  broken  up  into  smaller  gems.  On  account  of 
the  ready  cleavage  and  natural  brittleness  of  this  mineral 
it  is  very  easily  damaged  if  knocked  or  allowed  to  fall.  The 
powder  of  Fluor  Spar  of  any  colour,  if  sufficiently  fine,  is 
white,  hence  the  mineral  gives  a  white  "streak"  when 
drawn  over  a  harder  substance.  The  hardness  of  Fluor 
Spar  is  the  standard  No.  4  of  Mohs'  scale. 

The  crystalline  form  is  cubic,  and  crystals  may  have  the 
general  habit  of  the  cube  or  the  octahedron,  often  with  the 
edges  and  solid  angles  highly  modified  by  faces  of  other 
crystal  forms.  Crystals  occur  up  to  a  foot  or  more  across 
the  cube  face,  and  in  some  places  in  enormous  quantities. 


PRECIOUS   STONES.  143 

The  intimate  structure  of  the  crystals  may  be  in  the  form 
of  thin  lamellae  crossed,  thus  possibly  accounting  for  the 
anomalous  double  refraction  (Hussak).  Crystals  usually 
show  a  definite  point  of  attachment,  and  as  a  rule  form  a 
two-layered  coating  in  mineral  veins.  In  some  cases 
crystals  are  found  seemingly  perfectly  developed  all  over, 
but  these  have  very  likely  had  some  definite  point  of  attach- 
ment from  which  they  have  become  detached,  afterwards 
having  the  deficient  parts  made  up  before  the  circulation  of 
water  bearing  the  substance  in  solution  ceased. 

In  its  mode  of  occurrence  there  are  many  interesting 
points  to  notice.  By  far  its  most  common  situation  is  in 
the  mineral  veins  along  the  line  of  faults,  and  ^in  the 
fault-breccias  of  such  faults.  While  not  strictly  confined 
to  the  neighbourhood  of  calcareous  rocks,  there  is  yet  no 
doubt  that  it  is  more  often  found  in  such  relation  ;  its  dis- 
tribution in  such  a  vein  is  curiously  irregular,  it  may  be 
abundant  at  one  point  and  entirely  absent  a  short  distance 
above  or  below,  or  a  quarter  of  a  mile  further  along  the 
fault.  As  a  rule  there  is  evidence  of  it  having  been 
deposited,  at  nearly  the  same  time  as  many  of  its  associates, 
by  uprising  heated  waters  bearing  it  in  solution,  when  these 
waters  reached  such  a  point  that  relief  of  pressure  and 
decrease  of  temperature  made  it  no  longer  possible  for  the 
water  to  carry  so  much  mineral  in  solution.  These  deposits, 
in  most  cases  at  any  rate,  occurred  after  the  last  great 
movements  along  the  fault  ceased,  for  the  crystals  rarely 
show  any  sign  of  crushing.  Much  more  rarely,  deposits  of 
Fluor  Spar  occur  in  volcanic  rocks,  and  here  they  are 
probably  due  to  the  slow  solution  of  the  disseminated 
material  and  its  redeposition  in  a  seggregated  condition  at 


144  PEECIOUS  STONES. 

lower  levels.     An  interesting  case  is  that  of  the  Fluor  Spar 
occurring  in  geodes  at  Gourock  in  Scotland. 

The  associated  minerals  include  most  of  those  found  in 
mineral  veins,  the  commonest  being  Galena,  Quartz, 
Chalcopyrites,  Barytes,  Calcite,  etc. 

Its  chemical  composition  is  fluoride  of  calcium  Ca  F2. 
Chlorine  is  sometimes  present  in  traces,  and  the  colouring 
matter  is  usually  considered  to  be  a  compound  of  carbon 
and  hydrogen.  Enclosures  of  minute  grains  of  Quartz  are 
sometimes  seen,  and  the  blue  shades  with  a  greasy  lustre 
are  most  prone  to  contain  bubbles  of  liquid. 

Its  distribution  is  so  wide  that  only  the  more  important 
localities  can  be  indicated.  In  England  one  of  the  best 
localities^ is  the  district  of  Alston  Moor,  comprising  the 
great  upland  tract  to  the  east  of  Cross-fell.  Here  on  the 
old  "  Corpse-road  "  from  Garrigill  to  Kirldand,  Fluor  Spar 
from  the  adjacent  lead  mines  has  been  used  as  road  metal; 
and  to  one  who  is  fortunate  enough  to  be  passing  over  it 
when  the  sun  comes  out  after  a  shower,  the  sparkle  of 
colour  is  not  likely  to  be  forgotten.  From  the  mines  of 
Weardale  beautiful  violet  crystals  are  obtained.  Others,  of 
a  green  colour  by  transmitted  light,  show  the  property  of 
fluorescence  in  a  marked  degree,  turning  to  a  blue  when 
viewed  by  reflected  light.  Fine  honey-yellow  crystals  occur 
at  Scordale,  in  Westmorland.  Derbyshire  is  famous  for 
the  massive  variety  known  as  "  Blue  John,"  from  which 
vases  and  many  ornamental  objects  are  made.  This  variety 
is  particularly  fine  from  Tray  Cliff,  near  Castleton.  Corn- 
wall and  Devonshire  produce  crystals  having  a  wide  range 
of  colour.  Huel  Mary  Ann,  in  Cornwall,  is  noted  for  the 
beautiful  blue  crystals ;  also  Huel  Trelawney.  St.  Agnes 


PRECIOUS   STONES.  145 

yields  lilac  specimens.  In  North  Wales,  at  Moel-y-Cria, 
dark  amethyst-violet  crystals  occur.  At  Gourock,  in  Scot- 
land, both  purple  and  green.  In  Ireland,  from  Slieve  Game 
in  Antrim,  of  a  green  colour.  Yellow  crystals  of  various 
shades  are  found  at  Gersdorf  and  Freiburg,  in  Saxony. 
The  rare  rose-red  and  pink  crystals  are  found  in  the  Alps 
(St.  Gothard) ;  flesh-red  crystals  at  Miinstertbal,  in  Baden. 
Green  specimens  are  commoner ;  Petersburg,  near  Halle, 
and  Schlackenwald  may  be  cited;  also  Macomb,  in  New 
York  State.  Blue  crystals  are  found  in  the  salt-mines  in 
the  Tyrol,  and  the  tin-mines  of  the  Erzgebirge. 

Of  its  industrial  applications,  besides  its  use  as,,a  flux  in 
smelting,  the  manufacture  of  hydrofluoric  acid  is  dependent 
on  Fluor  Spar.  It  has  also  been  used  in  the  manufacture 
of  apochromatic  lenses. 

Its  use  in  jewellery  is  largely  in  imitation  of  rarer  minerals, 
which  it  resembles  in  colour,  and  when  used  for  this  pur- 
pose it  is  cut  after  the  style  that  is  usually  adopted  with 
the  gem  imitated.  Such  cut  specimens  are  styled  "  False 
Topaz,"  "False  Sapphire,"  etc.  Fluorescent  crystals  are 
sometimes  mounted  openly  ("  a  jour  ")  to  display  their 
varying  colour.  It  is  a  mineral  capable  of  receiving  a  high 
polish,  but  it  needs  great  care  in  handling.  Vases  made  of 
the  variety  "Blue  John"  can  be  turned  in  a  lathe  until 
very  thin  by  first  treating  the  material  with  resin  to  make 
it  more  durable ;  when  so  thinly  cut  the  colour  is  well 
seen.  The  purple  and  red  shades  are  often  produced 
artificially  by  heating  the  blue  and  violet  kinds;  it  has 
been  suggested  that  the  colour  is  here  due  to  the  presence 
of  two  hydrocarbons  of  different  degrees  of  volatility, 
that  which  causes  the  blue  shade  volatilising  at  a  lower 

p.s.  L 


146  PRECIOUS   STONES. 

temperature,  and  thus  leaving  behind  the  one  producing  a 
reddish  tint. 

210.  QUARTZ. 

This  mineral  is  more  abundantly  distributed  in  Nature 
than  any  other,  yet  though  so  plentiful,  in  its  different 
varieties,  it  is  largely  drawn  upon  to  provide  material  for  use 
as  precious  stones.  It  was  the  Crystallus  of  Pliny  and 
other  early  writers.  Theophrastus  mentions  it  as  one  of  the 
stones  set  in  rings.  Amongst  the  Komans  it  was  very 
highly  prized  for  the  purpose  of  making  vases  and  cups, 
and  fashion  decreed  that  such  "  crystal  cups  "  should  only 
be  used  for  iced  drinks,  hot  liquids  being  served  in  the 
Murrhine  vases  (King). 

The  known  varieties  of  this  mineral  are  so  many  that 
we  must  confine  the  general  account  of  the  physical  properties 
to  the  purer  forms,  and  point  out,  in  the  consideration  of 
the  different  kinds  that  more  particularly  concern  us,  any 
exceptional  features  in  which  they  differ  from  the  normal. 

Pure  Quartz  is  colourless,  but  small  amounts  of  impurities 
or  enclosures  may  give  it  various  shades  of  yellow,  brown, 
green,  red,  or  blue.  The  lustre  is  characteristically  vitreous, 
and  often  in  a  splendent  degree ;  some  kinds  have  a  greasy 
lustre.  The  diaphaneity  may  range  from  perfectly  trans- 
parent to  opaque.  It  shows  weak  double  refraction,  the 
indices  for  the  yellow  ray  being  1*544  and  1*553 ;  and  the 
dispersion  is  feeble  also,  the  refractive  index  of  the  ordinary 
my  for  red  light  being  1*541,  and  for  violet  light  1*558.  It 
follows  from  this  that  the  separation  of  the  two  images 
seen  on  looking  through  a  cut  piece  of  the  mineral  is  never 
great,  and  that  the  "  fire "  is  not  marked.  Also  if  the 


PRECIOUS   STONES.  147 

mineral  be  examined  under  the  polariscope  with  the 
Nicol's  prisms  crossed,  on  rotating  the  specimen  the  field 
becomes  lighter,  unless  viewed  along  the  optic  axis,  when 
all  remains  dark. 

It  is  moderately  diathermanous,  and  conducts  heat  well ; 
but  better  along  the  optic  axis  than  at  right  angles  to  it. 
It  is  very  infusible,  requiring  the  temperature  of  the  oxy- 
hydrogen  blowpipe  to  fuse  it.  A  difference  of  electric 
potential  is  developed  by  heat,  and  also  by  pressure.  Its 
electrical  resistance  is  high,  and  hence  it  is  useful  as  an 
insulator.  Fine  spun  threads  of  Quartz  retain  their 
insulating  properties  well,  even  in  moist  surroundings. 

The  specific  gravity  in  pure  forms  is  about  2*65  ;  in  some 
crypto-crystalline  forms  2 '60. 

Fracture :  Conchoidal  in  a  marked  degree  in  well 
crystallised  specimens;  some  massive  varieties  show  a 
splintery  or  flat  fracture.  Karely,  a  cleavage  parallel  to  the 
faces  of  the  positive  and  negative  rhombohedra  is  seen  ; 
the  frangibility  varies  from  brittle  to  tough.  The  hardness 
is  the  standard  7  of  Mohs'  scale.  The  streak  left  on  a 
harder  substance  is  white  in  the  colourless  varieties,  or  of 
a  pale  colour  in  other  kinds. 

Crystalline  Form  :  Quartz  belongs  to  the  rhombohedral 
division  of  the  hexagonal  system,  and  thus,  though  crystals 
appear  purely  hexagonal,  it  is  found  that  alternate  faces 
have  different  physical  properties  ;  often  the  rhombohedral 
character  is  marked.  The  commonest  type  of  crystal  is  a 
prism  terminated  at  one  or  both  ends  by  two  rhombohedra 
which  often  look  like  a  hexagonal  pyramid.  The  prism 
faces  may  be  long  or  entirely  absent ;  when  present  they 
often  show  transverse  marking.  It  is  noteworthy  that  the 

L  2 


148 


PKECIOUS  STONES. 


basal  face,  or  plane  normal  to  the  vertical  axis,  is  only  very 
rarely  seen ;  crystals  may  be  highly  modified  by  many 
crystal  forms.  The  more  purely  crystallised  varieties 
usually  show  a  point  of  attachment  at  one  end  of  the 
vertical  axis.  Twinned  crystals  are  often  seen. 

In   its   origin,    Quartz    shows   great  variety.     It   is    an 
original  constituent  of  most  volcanic  rocks,  but  the  kinds 


FIG.  12. — Quartz  :  Var.  Rock  Crystal.     From  Dauphine. 

we  have  to  deal  with  more  particularly  are  usually  the 
result  of  solution  of  the  disseminated  mineral,  or  of  the 
decomposition  of  silicates,  and  redeposition  in  larger  masses. 
The  wonderful  groups  of  Rock  Crystal  found  in  fissures  in 
the  rocks  of  the  Alps,  originated  in  this  manner.  It  is  a 
common  constituent  of  mineral  veins,  more  often  as  a 
deposit  from  uprising  heated  waters,  but  sometimes  as  a 
later  infiltration  probably  from  above, 


PF-HE 

UNIVERSITY 

OF 


STONES.  i49 

From  the  varied  origin  it  will  be  seen  that  its  associates 
may  be  almost  any  other  known  mineral. 

Chemical  Composition :  Silicon  dioxide,  Si02.  Impure 
forms  may  contain  clay,  oxide  of  iron  and  many  other  sub- 
stances. Inclusions  are  common  and  will  be  referred 
to  below.  Although  Quartz  by  itself  is  so  infusible,  it  is 
readily  fused  when  mixed  with  an  alkaline  carbonate, 
but  this  is  a  chemical  action  and  results  in  the  forma- 
tion of  an  alkaline  silicate  ("  water-glass  ")  which  is  soluble 
in  water. 

A.  PHENO-CRYSTALLINE  OR  VITREOUS  VARIETIES. 
1.  Eock  Crystal  is  the  ordinary  colourless  variety;  it  is 
always  crystalline  and  often  crystallised.  The  crystals  are 
usually  elongated,  and  of  sizes  varying  from  a  small  pin  to 
several  feet  in  length.  Fresange  records  a  crystal  from 
Madagascar  measuring  20  feet  in  circumference.  Dauphine 
(Bourg  d'Oisans)  is  famous  for  its  groups  of  Rock 
Crystal  (Fig.  12).  The  Alps  generally  have  afforded  fine 
specimens,  and  a  notable  group  in  the  Museum  at  Naples 
maybe  mentioned.  In  1719  a  cavity  was  found  at  Zinken, 
in  the  Bernese  Obeiiand,  from  which  crystals  weighing 
altogether  50  tons  were  taken,  and  sold  for  some 
£60,000,  some  of  the  crystals  weighing  up  to  8  hundred- 
weight. In  Upper  Valais,  crystals  were  found  in  a  cavity 
which  were  of  extraordinary  size,  up  to  over  half  a  ton  in 
weight.  The  Carrara  marble  quarries  have  also  afforded 
good  specimens.  A  specimen  in  Paris,  taken  by  the  French 
in  Italy  in  1797,  weighs  8  hundredweight  and  is  3  feet  in 
diameter.  The  Caucasus,  Siberia,  Brazil,  and  particularly 
Japan,  have  produced  fine  specimens.  In  North  America, 


150  fKECfOUS  STONES. 

Moose  Mountain,  in  New  Hampshire,  may  be  cited  as  a 
locality. 

The  so-called  "  Bristol  Diamonds  "  belong  to  this  variety 
of  Quartz,  and  so  does  the  "Brazilian  pebble."  Lake 
George,  in  New  York,  has  also  given  its  name  to  "  Lake 
George  Diamonds."  Many  other  localities  have  also  had 
their  names  used  in  this  way.  Speaking  generally,  when 
Bock  Crystal  is  cut  to  simulate  Diamond,  the  word  "  occi- 
dental "  is  prefixed.  The  real  nature  of  the  mineral  may 
be  recognised  by  its  lower  specific  gravity  than  other 
colourless  precious  stones,  by  its  hardness  being  exactly  7, 
and  by  its  want  of  fire.  From  Diamond  and  colourless 
Spinel  it  differs  in  being  doubly  refracting. 

The  applications  of  this  variety  in  the  Arts  are  numerous. 
As  Quartz  sand  it  enters  largely  into  the  composition  of 
better  qualities  of  glass,  and  now  pure  fused  Quartz  is  being 
used  for  some  special  purposes  where  glass  was  used 
previously.  The  fashionable  ladies  of  ancient  Borne  used 
it  to  cool  their  delicate  hands  with,  for  this  purpose  carrying 
small  spheres  of  Bock  Crystal  in  hot  weather.  Pliny  was 
informed  that  a  ball  of  it  formed  the  best  means  of  cauteris- 
ing any  part  of  the  body  by  physicians,  the  patient  being 
placed  in  sunshine  for  this  operation,  and  the  rays  passing 
through  the  sphere  brought  to  a  focus  at  the  desired  point. 
King  ("Precious  Stones")  amongst  a  wealth  of  other  illustra- 
tions of  its  use  in  past  times  quotes  an  amusing  dialogue  in 
Aristophanes  in  which  the  use  is  suggested  of  a  Crystal 
sphere  to  conveniently  dispose  of  an  unwelcome  writ.  The 
use  of  "  Brazilian  pebble  "  in  the  manufacture  of  spectacle 
lenses  has  long  been  known.  Bock  Crystal  is  also  used  in 
lamps  for  some  forms  of  light  treatment  in  medicine.  Fine 


PRECIOUS  STONES.  151 

fibres  spun  from  a  bead  of  molten  Quartz  are  used  to  suspend 
the  magnets  in  delicate  galvanometers,  since  they  allow  the 
magnets  to  return  very  readily  to  the  position  of  rest  when 
no  current  is  passing.  The  Chinese  make  buttons  of  it. 

In  ancient  times  it  was  highly  valued,  especially  perhaps 
by  the  Komans,  for  the  production  of  vases  and  cups,  some 
of  which  were  of  remarkable  size,  for  it  is  recorded  by  Ben 
Mansur  that  at  the  capture  of  Ghasna  in  1159  four  vases 
made  of  Kock  Crystal  were  found,  each  of  which  would  hold 
two  skinfuls  of  water.  Pliny  records  that  the  material  then 
used  came  from  the  Alps,  and  at  that  time  it  was  believed 
to  be  water  frozen  so  hard  that  it  could  not  be  thawed  at 
ordinary  temperature ;  this  is  said  to  have  led  the  Komans 
to  only  use  it  for  cold  liquids.  One  of  the  most  beautiful 
pieces  of  work  in  this  material  was  a  vase  belonging  to  the 
French  Kings  ;  it  was  9  inches  high  and  9J  inches  in 
diameter,  and  was  carved  with  figures  illustrating  the 
intoxication  of  Noah.  It  cost  some  ^64,000. 

The  Indians  used  the  material  also  in  the  production  of 
imitations  of  the  rarer  gems,  for  this  purpose  staining  it  in 
various  ways;  but  though  these  methods  seem  to  have  been 
known  to  Pliny,  he  declines  to  record  them,  on  the  ground 
that  they  were  fraudulent.  Dutens  ("Pierres  Precieuses") 
states  that  the  methods  were  as  follows :  The  Kock  Crystal 
was  made  red  hot  and  then  plunged  into  various  coloured 
solutions.  By  this  means  innumerable  minute  cracks  were 
produced,  into  which  the  coloured  liquid  penetrated.  The 
colours  used  were  :  for  Kuby,  tincture  of  cochineal ;  for 
Topaz,  tincture  of  saffron ;  for  Sapphire,  tincture  of 
Turnesol;  for  Amethyst,  the  juice  of  Nerprum  ;  by  using 
-both  Turnesol  and  saffron,  an  emerald-green  was  produced. 


152  PRECIOUS  STONES. 

A  cold  method  consisted  in  soaking  the  crystal  in  a  solution 
of  the  coloured  resins  in  turpentine  or  alcohol ;  how  stain- 
ing occurs  in  this  case  is  not  clear,  as  ordinary  Eock  Crystal 
will  not  absorb  colour ;  still,  the  Indians  seem  to  have  had 
some  secret  method  of  uniformly  staining  Quartz.  More 
simple  methods  were  to  coat  the  lower  part  of  the  cut  stone 
with  some  coloured  varnish,  and  then  mount  it  in  a  closed 
setting.  The  clear  colourless  varieties  were  nearly  always 
set  -with  foil  at  the  back. 

The  sub-variety  known  as  Iris  or  Eainbow  Quartz,  is 
ordinary  Kock  Crystal  containing  fine  flaws,  into  which  air 
has  penetrated  as  a  very  thin  film,  giving  rise  to  the  optical 
effect  of  colour  as  seen  in  Newton's  rings  and  in  thin  soap 
bubbles.  The  flaws  may  be  present  when  found,  or  they  may 
be  induced  by  a  blow  or  by  cooling  suddenly  after  heating. 
It  is  cut  with  a  low  curved  surface  kept  as  close  to  the  flaw 
as  possible. 

Iridescent  Quartz  is  Kock  Crystal  with  a  thin  film  of 
some  mineral  on  the  surface  of  the  crystals ;  this  film  often 
consists  of  Limonite  or  other  oxide.  If  used  for  ornamental 
purposes  it  must  be  kept  in  its  natural  state,  as  the 
beautiful  colour  is  only  a  surface  effect.  Very  fine  colours 
are  seen  on  some  of  the  Quartz  from  the  Caldew  in 
Cumberland. 

2.  The  variety  known  as  Asteriated  or  Star  Quartz,  shows 
a  six-rayed  star  when  cut  normal  to  the  vertical  axis,  similar 
to  the  Asteriated  Sapphire. 

3.  Amethyst,  Quartz  of  a  violet  colour. 

Although  the  name  is  usually  derived  from  a  and  ptOv , 
that  is  "  without  wine,"  King  suggests  it  is  more  likely  that 
the  Greeks  adopted  an  Oriental  name,  and  derived  their 


t>BECtOtrs  STONES.  153 

Own  term  from  it ;  and  further,  attributed  to  it  the  property 
of  being  an  antidote  for  intoxication.  It  is  sometimes  desig- 
nated "occidental  Amethyst"  to  distinguish  it  from  the 
very  rare  amethyst-coloured  Corundum,  to  which  the  term 
"  Oriental  Amethyst  "  is  applied.  It  is  often  rather  turbid 
in  colour,  and  not  infrequently  alternate  layers  of  colourless 
and  amethystine  Quartz  may  be  seen  in  one  crystal.  Such 
kinds  as  are  transparent  and  of  a  good  even  colour  suitable 
for  use  as  gems,  are  designated  "precious  Amethyst." 
Good  specimens  were  held  in  very  high  repute  by  the 
ancients — too  valuable  to  be  engraved  as  most  of  their 
precious  stones  were.  Now,  however,  it  is  of  little  value, 
though  even  a  hundred  years  ago  it  was  much  prized,  and 
Queen  Charlotte's  necklace  of  fine  Amethysts  was  valued  at 
^£2,000 ;  now  the  very  best  qualities  are  only  worth  10s.  a 
carat,  or  less. 

In  addition  to  its  presumed  virtue  in  allowing  of  liberal 
potations  without  unpleasant  effects,  it  was  reputed  to 
enable  the  wearer  to  interpret  dreams,  maintain  presence 
of  mind,  and  cast  off  evil  thoughts,  and  so  on. 

It  was  the  eighth  stone  of  Aaron's  breastplate,  and  it  has 
from  its  use  as  a  ring  stone  by  Bishops  of  the  Koman 
Church,  been  called  "  Bishop's  Stone." 

Amethyst  exhibits  a  feeble  dichroism,  the  images  being  a 
reddish-violet  and  bluish-violet  respectively. 

It  usually  occurs  in  short  prisms  with  the  two  rhorn- 
bohedra,  or  even  without  the  prism  form  at  all.  As  indicated 
in  the  section  dealing  with  the  origin  of  precious  stones  in 
general,  Amethyst  is  often  found  in  vapour  cavities  in  lavas, 
sometines  lining  the  unfilled  portion  of  an  Agate ;  it  also 
occurs  similarly  to  vein  Agate,  deposited  in  fissures  by 


154  PRECIOUS  STONES. 

downward  percolating  water.  The  formation  of  one  pound 
of  Amethyst  in  a  vapour  cavity  has  been  estimated  to 
occupy  over  one  and  a  quarter  million  of  years  (Kudler, 
"  Pop.  Science  Keview,"  Vol.  I.). 

What  the  colour  is  due  to  is  not  absolutely  certain,  but 
probably  most  specimens  owe  it  to  the  presence  of  traces 
of  manganese  compounds,  which  impart  an  almost 
identical  tint  to  glass  when  fused  with  it.  Manganese 
is  certainly  present  in  many  Amethysts,  though  in  very 
small  percentages,  a  deep  coloured  stone  only  showing 
O'Ol  per  cent.  (Heintz).  The  colour  is  easily  discharged 
by  heat. 

It  is  found  in  many  localities.  In  England,  chiefly  in 
the  south-western  counties — Cornwall,  Devon,  Somerset  and 
Gloucester.  In  Scotland,  at  many  places,  as  Loch  Morar  in 
Inverness-shire,  Campbeltown  in  Argyllshire,  etc.  Ireland, 
near  Cork,  and  on  Achill  Island,  both  providing  fine  speci- 
mens. Abroad,  at  Oberstein,  there  was  at  one  time  a 
plentiful  supply,  but  now  it  is  exhausted,  though  the  chief 
seat  of  the  cutting  industry  is  still  there,  the  material  being 
imported  from  Brazil,  where  it  is  found  in  large  amount. 
Thus  in  the  Serra  do  Mar  a  cavity  was  found  containing 
35  tons  of  Amethyst  in  1900  (Max  Bauer).  Uruguay 
also  provides  a  good  deal.  At  Mursinka  in  the  Urals  it  is 
largely  worked,  here  occurring  in  veins  and  cavities  in 
decomposed  granite,  other  cavities  at  greater  depths  con- 
.taining  Beryl  and  Topaz.  Transylvania  also  yields  a  certain 
amount.  In  China  large  crystals  are  found,  but  most  of 
them  are  turbid.  Ceylon  yields  the  finest  qualities,  it  being 
here  found  in  gravels  derived  from  the  weathering  of  granite 
rocks,  associated  with  many  other  gem  stones.  In  North 


STONES.  loo 

America,  near  Greensboro  in  North  Carolina,  in  the  districts 
around  Lake  Superior,  especially  the  north-west. 

It  is  usually  step-cut  and  mounted  a  jour.  A  massive 
variety,  called  Prime  d'Amethyst,  is  cut  into  cups  and 
vases. 

4.  Kose  Quartz  is  a  pink  or  pale  red  variety,  usually 
showing  a  vitreous  lustre  and  small  conchoidal  fracture ; 
usually  not  crystallised,  and  but  rarely  transparent.      Its 
colour  is  due  to  traces  of  titanic  oxide,  and  is  prone  to  fade 
on  exposure,  though  it  may  to  some  degree  be  restored  by 
moistening  the  specimen.     When  of  fine  colour  it  may  be 
cut  and  sold  as  "  Bohemian  Kuby  " ;  more  often  it  is  cut  into 
plaques  with  a  curved  upper  surface.     It  is  rather  a  rare 
variety.     Localities  where  it  is  found  are  Eabenstein  and 
Konigswerth  in  Bavaria,  Ekaterinburg  in  the  Urals,  and 
Beinn  Doireann  in  Scotland.    It  is  distinguished  from  glass 
imitations  by  its  hardness  and  double  refraction. 

5.  Yellow  Quartz,  or  Citrine,  is  a  variety  that  is  often 
used  to  imitate  yellow  Topaz,  which  it  much  resembles  in 
colour,  hence  it  is  often   called  "  Occidental   Topaz  "  or 
"  Spanish   Topaz."      Like   Eose  Quartz,  it   is  one  of  the 
rarer  varieties.       Scottish  localities   are  Loch  Avon  and 
Goatfell ;  in  France  at  Bourg  d'Oisans  ;  mostly  found  in 
Brazil  and  Uruguay  (often  with  Amethyst),  and  is  thence 
sent  to  Oberstein  to  be  cut.   In  the  Sierra  Morena  in  Spain 
a  variety  which  assumes  a  good  yellow  colour  on  heating  is 
found  ;  this  is  cut  and  sold  as  "  Spanish  Topaz."     It  is  dis- 
tinguished from  Topaz  when  in  the  rough  state  by  its  want 
of  cleavage  and  by  being  softer.     When  cut  it  may  be  dis- 
tinguished  by  its   lower   specific   gravity  and  very  weak 
dichroism. 


156  EBEOlOtJS   STONES. 

6.  Smoky  Quartz,  or  Cairngorm,  derives  its  alternate 
name  from  the  Cairngorm  mountains  in  Scotland,  where  it 
occurs  in  numerous  places.  It  is  the  Mormorion  of  Pliny, 
but  Morion  is  now  rather  restricted  to  the  dark  opaque 
varieties.  In  colour  it  varies  from  a  pale  sherry  tint 
through  all  degrees  of  smoky  brown  to  almost  black. 
Transparent  to  opaque;  the  darker  coloured  specimens  show 
a  distinct  dichroism,  one  image  being  yellow-brown  and  the 
other  a  purer  warm  brown.  It  occurs  in  crystals  identical 
in  all  respects  except  colour  to  Kock  Crystal ;  its  commonest 
mode  of  occurrence  is  in  fissures  in  granite  and  allied  rocks  ; 
sometimes  in  spaces  in  the  outer  parts  of  a  granitic  mass, 
probably  due  to  shrinkage  on  consolidation ;  in  such  cavities 
sometimes  associated  with  Beryl,  Topaz,  and  crystals  of 
Felspar. 

The  colour  is  due  to  disseminated  volatile  compounds  of 
hydrogen  and  nitrogen,  which  are  largely  discharged  at  a 
comparatively  low  temperature,  so  that  specimens  which 
are  naturally  too  dark  to  use  as  gems  may,  by  boiling  in 
oil,  be  brought  to  a  rich  colour  and  rendered  transparent. 
One  crystal  of  very  dark  colour  in  the  Eoyal  Scottish 
Museum  was  so  treated  by  Professor  Heddle  fourteen 
times,  but  without  attaining  the  desired  result ;  this,  how- 
ever is  exceptional.  Usually  by  raising  the  temperature  to 
200°  C.  the  colour  is  completely  discharged. 

Of  the  Scottish  localities,  Cairngorm  and  other  hills  of 
that  range  provide  good  crystals,  also  Stirling  Hill  in 
Aberdeenshire,  and  Beinn  a  Bhuird  in  the  same  county. 
Very  beautiful  crystals  are  found  in  the  Goatfell  granite  in 
Arran.  The  somewhat  similar  granite  of  the  Mourne 
Mountains  in  Ireland  yields  beautiful  specimens.  The 


PRECIOUS  STONES.  157 

central  Alps  provide  the  largest  crystals,  some  from  the 
Tiefen  Glacier,  found  in  1868,  measuring  nearly  26  inches 
in  length ;  one  of  the  best  of  the  specimens  is  now  in  the 
Museum  at  Berne;  altogether  some  15  tons  of  crystals 
were  found  in  this  one  cave.  One  specimen  in  the  national 
collection  in  the  British  Museum  is  over  3  feet  long. 
Other  localities  are  Mursinka  in  the  Urals,  where  also 
Amethyst  is  found  ;  and  with  Amethyst  and  other  precious 
stones  in  the  gravels  in  Ceylon.  North  American  localities 
include  Paradise  Biver,  in  Nova  Scotia ;  Pike's  Peak  in 
Colorado;  Magnet  Cove,  Arkansas;  Goschen,  Massachussets. 

It  is  usually  step-cut,  sometimes  brilliant-cut.  In  Scot- 
land it  is  largely  used  in  the  mounting  of  Highland  dress 
accoutrements. 

Its  specific  gravity  alone  is  sufficient  to  distinguish  it 
from  other  gem  stones  of  the  same  colour.  In  addition  its 
hardness  and  faint  dichroism  would  distinguish  it  from  any 
glass  imitation. 

7.  Milky  Quartz  is  a  crystalline  variety,  showing,  as  its 
name  implies,  a  milky  colour.     It  is  not  important  in  the 
present  relation. 

8.  Sapphire  Quartz,  or   Siderite,   also   known  as   Azure 
Quartz,  is  a  blue  variety,  showing  a  finely  fibrous  enclosure ; 
it  is  rarely  cut  as  a  gem  stone ;  it  is  found  in  an  impure 
limestone  at  Golling,  in  Salzburg. 

9.  Sagenitic  Quartz  is  a  crystalline  variety,  containing 
enclosures  of  minerals  in  fine  needles.     The  forms  met  with 
in  use  as  gems  are  also  known  as  Needle  Stone,  Venus'  Hair 
Stone,  and  Fleches  d' Amour.  The  substance  enclosed  may  be 
Rutile  or  Gothite  in  the  Venus'  Hair  Stone  ;  coarser  acidular 
crystals  of  Rutile  are  seen  in  the  Needle  Stone,    Fibres  of 


158  PRECIOUS  STONES. 

Actinolite  or  other  members  of  the  Amphibole  group  occur 
in  the  kind  known  as  Thetis'  Hair  Stone.  The  high 
adamantine  lustre  and  rich  reddish-brown  colour  of  the 
Eutile  crystals  give  a  striking  effect  when  contained  in  a 
polished  piece  of  clear  Quartz  (Fig.  18). 

Madagascar  yields  specimens  containing  Manganite  and 
Hornblende.      Quartz   with   needles   of   Gothite   is    found 


FIG.  13.— Quartz  :  Var.     Venus'  Hair  Stone. 

near  St.  Petersburg ;  that  with  Eutile  occurs  in  Savoy  and 
Switzerland. 

10.  Coming  under  this  head,  but  worthy  of  separate 
mention,,  is  the  variety  known  as  Cat's  Eye,  further  dis- 
tinguished from  Cymophane,  a  variety  of  Chrysoberyl,  as 
Quartz  Cat's  Eye,  or  Occidental  Cat's  Eye.  It  is  crystalline 
Quartz,  containing  delicate  closely-packed  and  parallel  fibres 
of  Asbestos,  which  give  it  a  greenish  or  grey  tint.  On 


PEECIOUS   STONES.  159 

turning  the  specimen  about,  however,  a  wave  of  milky 
white  light  is  seen  to  cross  the  stone,  due  to  reflection  from 
the  innumerable  fibres  of  Asbestos.  In  some  cases  the 
Asbestos  has  been  removed  from  the  more  durable  Quartz 
by  weathering,  and  thus  a  series  of  minute  tubes  are  left. 
These,  however,  give  the  same  optical  effect. 

Most  specimens  are  from  India  and  Ceylon  ;  in  the  latter 
locality  the  mineral  occurs  in  the  gem  gravels  as  pebbles. 

It  is  usually  cut  en  caboclioti,  with  the  lower  surface 
parallel  to  the  fibres  ;  on  turning  the  stone  the  band  of 
light  is  seen  to  move  across ;  the  ideal  is  to  have  the  light 
band  as  narrow  and  bright  as  possible. 

11.  Aventurine  is  a  sub- transparent  to  sub-translucent 
Quartz,  containing  numerous  scales  of  some  glittering 
mineral,  which  may  be  Mica,  Haematite,  Limonite,  or  other 
mineral.  The  Quartz  is  colourless,  but  the  enclosures  are 
usually  a  golden  or  muddy  brown,  sometimes  silvery  or 
green,  rarely  blue.  The  flakes  of  the  enclosed  mineral  are 
often  arranged  in  a  definite  way,  so  that  on  turning  the 
specimen  a  brilliant  metallic  reflection  is  obtained.  It  is 
sometimes  distinguished  from  tbe  Aventurine  varieties  of 
the  Felspars  by  calling  it  Quartz  Aventurine.  When  cut  as 
a  gem  it  is  usually  given  a  low,  rounded  surface  ;  more  often 
it  is  used  for  the  production  of  vases  and  similar  objects. 

Amongst  the  localities  where  it  is  found  Pliny  mentions 
it,  under  the  term  Corallachates,  as  coming  from  Crete. 
There  is  a  possibility  that  the  Sandaster  of  Pliny  may  have 
been  Aventurine  in  part.  In  Scotland  it  occurs  on  Ben 
Hope,  in  Sutherland,  coloured  by  a  red  Mica  and  red 
Zircon  ;  also  on  Ben  Eibhinn,  in  Inverness-shire.  In  Spain 
it  is  found  at  Cape  de  Gatte;  at  Nantes,  in  France;  in 


160  PEECTOUS  STONES. 

Piedmont ;   in  the  Urals  at  Kossulina  and  Kolivan ;  near 
Bellary,  in  India. 

It   is   distinguished   from   the   Aventurine   varieties    of 
Felspar  by  its  greater  hardness. 

12.  Varieties    containing   impurities    are    not   of    much 
importance  in  the  present  relation,  though  a  few  used  to 
be  cut  at  the  beginning  of  the  eighteenth  century.     The 
only  kinds  we   need  consider  are :    (1)  Quartz,  containing 
Gold  in  the  form  of  filaments,   or  scattered  particles;  in 
America  a  considerable  amount  is  cut  for  use  as  a  fancy 
stone ;  but  elsewhere  it  is  not  often  used,  except  by  those 
who  have  had  to  do  with  gold-mining.     Material  suitable 
for  this  purpose  is  found  in  Australia,  South  Africa,  and 
particularly  in  the  Western  States  of  America.     Similar 
inclusions  of  Silver  are  very  rare.     (2)  Quartz  containing 
Haematite.      This  is  known  also  as    Sinople,  Hyacinth  of 
Compostella,  and  Eisenkiesel.     It  is  Quartz  richly  impreg- 
nated with  the  red  oxide  of  iron,  Haematite,  from  which  it 
derives  its  blood-red  colour.     It  has  been  used  to  imitate 
the  variety  of  Zircon  called  Hyacinth,  but  is  distinguished 
from  it  by  its  inferior  specific  gravity.     It  is  found  in  beds 
of  Gypsum  at  Compostella,  in  the  north  of  Spain ;  also  in 
Saxony,  Bohemia,  and  Hungary.     The  iron  mines  of  West 
Cumberland    afford    some    very   beautiful   specimens,   the 
colour  in  them  possibly  being  due  to  Turgite,  and  not  to 
Haematite.      The  Compostella  specimens  usually  occur  in 
short  prisms,  with  a  termination  at  each  end. 

13.  Quartz  containing  Liquids  in  Cavities.     These  forms, 
though  of  considerable  scientific  interest,  are  rarely  used 
now  for  ornamental  purposes.     Some  are  cut  in  the  United 
States  as  curiosities. 


PEECIOUS  STONES.  161 

B.  CRYPTOCRYSTALLINE  VARIETIES. 

All  these  consist  of  a  mixture  of  silica  in  a  colloid  or 
opaline  form,  and  silica  in  some  crystalline  form,  which  has 
been  termed  Quartzine,  and  without  or  with  added 
impurities. 

1.  Chalcedony  may  be  regarded  as  the  mixture  denned 
above,  without  any  impurities.  It  is,  so  to  speak,  the 
foundation  material  from  which,  by  the  intermixture  of 
various  other  substances,  all  the  further  cryptocrystalline 
varieties  of  silica,  as  Agate,  Heliotrope,  Carnelian,  Jasper, 
etc.,  result. 

The  origin  of  the  name  is  difficult  to  trace.  It  seems  to 
have  come  to  be  applied  to  the  mineral  we  now  know  under 
this  name  by  a  slowly  evolved  confusion,  for  the  Chalce- 
donius  of  Pliny  would  appear  to  be  Dioptase  from  the  copper 
mines  of  Chalcedon.  The  Leucachates  of  Pliny  and  laspis 
of  Theophrastus  would  seem  to  be,  in  part  at  any  rate,  our 
Chalcedony. 

The  colour  is  characteristically  a  white  or  greyish-white, 
but  minute  traces  of  impurities  are  sufficient  to  alter  the 
colour,  when  distinctive  names  are  often  applied.  The 
lustre  is  waxy  to  slightly  greasy.  Not  being  of  a  definite 
crystalline  structure  like  Quartz,  it  lacks  the  special 
properties  of  Quartz  dependent  on  that  structure ;  further 
its  specific  gravity  is  rather  lower,  2*59 — 2'60.  The  hard- 
ness only  equals  about  6J.  Its  fracture  is  flat,  and  often 
rather  splintery.  It  is  transparent  in  only  a  few  cases,  more 
often  sub-transparent,  or  only  translucent.  It  has  no 
definite  crystalline  form  of  its  own,  though  often  found 
pseudo-morphous  after  other  minerals.  In  intimate 

p.s.  M 


162  PEECIOUS   STONES. 

structure  it  shows  a  finely  fibrous  arrangement,  which 
may  be  only  seen  under  the  microscope,  or  may  be  apparent 
to  the  unaided  eye.  It  occurs  in  rounded  masses  (mam- 
millated  or  botryoidal),  sometimes  in  stalactites,  more 
often  in  cavities  in  rocks. 

The  history  of  its  origin  introduces  us  to  so  many 
features  of  interest  in  the  consideration  of  the  origin  of  the 
large  groups  of  minerals  formed  by  downward  percolating 
water,  that  it  has  been  described  in  detail  when  speaking 
of  the  origin  of  precious  stones  in  general. 

Chemically  it  is  essentially  silicon  dioxide,  but  many 
specimens  are  found  to  contain  some  water,  varying  in 
amount  from  practically  nothing  till  it  approaches  the 
quantity  contained  in  Opal  (q.  v.).  The  general  appearance 
of  the  mineral  differs  somewhat  with  this  varying  per- 
centage of  water.  Under  the  influence  of  solvents,  such  as 
alkaline  solutions,  it  shows  a  greater  readiness  of  solution 
than  Quartz.  Bands  having  different  degrees  of  porosity 
are  common. 

It  is  of  very  wide  distribution  in  rocks  of  volcanic  origin, 
which  have  been  subjected  to  some  disintegration  by  water 
acting  chemically.  The  best  specimens  come  from  the 
Faroe  Islands,  Iceland  and  India. 

Chalcedony  has  been  much  used  for  vases,  cups,  beads, 
dishes,  etc.  When  cut  for  a  ring  stone  or  a  brooch,  it  gives 
the  finest  surface  if  the  cut  is  across  the  fibre  of  the  mineral. 
It  is  sometimes  stained  before  cutting,  but  not  so  frequently 
as  the  sub-variety  Agate,  hence  the  staining  will  be 
considered  under  "  Agate." 

2.  Carnelian. — This  is  Chalcedony  coloured  by  the  oxide 
of  iron,  Haematite  ;  it  was  the  Sardius  of  old  writers,  and 


PRECIOUS  STONES.  163 

is  still  sometimes  called  Sard.  Except  in  the  matter  of 
colour,  it  has  the  same  properties  as  Chalcedony,  and  it 
occurs  either  as  an  ordinary  Agate,  or  in  fissures  as  Vein 
Agate.  Although  of  wide  distribution,  the  chief  localities 
are  only  two.  In  India  it  is  found  in  the  Eajpipla  hills  on 
the  river  Nerbudda;  also  on  the  Mahi  river,  north  of 
Baroda.  When  found  in  situ,  the  colour  is  usually  very 
dark,  sometimes  almost  black,  sometimes  greenish,  but  on 
heating  it  assumes  its  well  known  red  colour;  it  is  con- 
sidered that  a  better  colour  results  by  exposing  to  the  rays 
of  the  sun,  the  process  requiring  as  long  as  two  years.  It 
is  cut  at  Cambay. 

In  Brazil  it  is  found  at  Campo  de  Maia,  associated  with 
Agate.  Arabia,  New  Zealand,  Scotland,  Saxony  and  many 
other  parts,  also  yield  this  variety.  Pliny  mentions  a  mine 
of  Sard  at  Babylon. 

The  modern  name  Carnelian  was  given  to  it  on  account 
of  its  flesh-colour.  Inferior  coloured  specimens  may  be 
improved  by  soaking  in  a  solution  of  an  iron  salt  and  then 
heating  to  produce  the  ferric  oxide.  It  is  rather  curious 
that  this  variety  containing  iron  should  have  been  held  to 
be  specially  emcaceous  in  the  healing  of  wounds  inflicted  by 
iron  instruments.  Epiphanius  also  mentions  its  value  for 
the  cure  of  tumours. 

It  has  always  been  a  favourite  substance  in  which  to 
carve  devices  for  use  as  signets,  and  Pliny  mentions  the  ease 
with  which  it  left  the  wax  then  used  for  sealing. 

3.  Chrysoprase  is  the  variety  coloured  green  by  Nickel. 
It  is  not  the  same  as  the  Chrysoprasius  of  Pliny,  which  was 
probably  Peridot ;  the  Chrysoprase  we  know  seems  to  have 
been  unknown  to  the  ancients.  It  occurs  in  veins  in  a 

M  2 


164  PRECIOUS   STONES. 

serpentinous  decomposition  product  at  Kosemiitz  in  Silesia, 
specimens  from  which  showed  0*5  to  1*0  per  cent,  of  nickel 
oxide  on  analysis.  The  colour  is  destroyed  by  moderate 
heat  and  also  by  strong  light;  if  used  as  a  seal  to  any  great 
extent  much  of  the  colour  is  discharged,  but  it  can  be 
regained  to  a  large  degree  by  soaking  the  stone  in  water  ; 
the  colour  is  supposed  to  be  due  to  nickel  in  the  form  of  a 
hydrous  silicate,  and  colourless  Chalcedony  can  be  made  to 
very  closely  simulate  Chrysoprase  by  impregnating  it  with 
a  solution  of  a  green  nickel  salt.  There  is  a  locality  where 
it  occurs  in  India,  but  it  is  not  known  definitely,  and  other 
occurrences,  though  widespread,  are  not  of  great  importance. 
At  one  time  it  was  a  very  fashionable  stone,  then  its  use 
almost  entirely  died  out,  but  in  recent  years  it  has  again 
come  somewhat  into  favour.  It  is  usually  cut  in  a  low 
rounded  form,  often  with  one  or  two  rows  of  facets  above 
the  girdle. 

4.  Prase  is  a  dark  green  variety ;  some  forms  of  crystal- 
line Quartz  of  the  same  colour  are  also  known  as  Prase. 
It  is  translucent,  and  owes  its  colour  to  fine  filaments  of 
Actinolite  as  a   rule.      It  was   a   favourite   substance   for 
engraving  in  Roman  times,  and  is  still  sometimes  so  used ; 
also  cut  into  flat  pieces  for  inlaying.     Saxony  and  Scotland 
may  be  mentioned  as  two  of  the  numerous  localities.     This 
was  the  Heliotrope  of  Pliny. 

5.  Plasma  is  a  form  of  Chalcedony  containing  a  chloritic 
or  asbestos-like  mineral,  or  what  is  known  as  Green  Earth 
(Delessite  or  Saponite).     It  was  the  laspis  of  Pliny  in  part. 
In  colour  it  varies  from  a  dull  leek-green  to  almost  emerald- 
green,  often  showing  white  spots.     It  was  fashioned  by  the 
Eomans,  but  now  is  seldom  used ;  the  best  specimens  come 


PRECIOUS   STONES.  165 

from  the  Deccan  in  India  and  the  first  cataract  of  the  Nile; 
though  fairly  common  in  many  other  places,  the  quality  is 
not  so  good. 

Bloodstone  is  the  same  as  the  above,  but  with  small  red 
spots.  Heliotrope,  again,  is  similar  with  rather  larger  spots 
of  red  ;  it  was  the  Prasius  of  Pliny.  The  best  qualities 
have  bright  red  well-defined  spots  on  a  uniform  translucent 
ground  of  dark  green.  Such  specimens  are  found  in  India, 
west  of  Cambay;  also  at  Creag  nan  Stardean  in  Eum,  one 
of  the  Inner  Hebrides. 

6.  Agate. — Most  Agates  consist  entirely,  or  almost  entirely, 
of  crypto-crystalline  silica  ;  but  from  this  normal  type  many 
departures  are  to  be  recognised,  and  thus  as  the  term 
Agate  is  now  used  it  has  reference  rather  to  the  origin 
of  the  stone  than  its  special  variety ;  thus  true  Agates 
are  all  formed  in  the  steam  cavities  of  eruptive  rocks, 
usually  lavas ;  it  is  a  curious  fact  that  Agates  are  practically 
only  found  in  rocks  whose  percentage  of  silica  is  about  45 
or  50,  and  by  no  means  all  rocks  having  this  amount  of 
silica  contain  Agates.  The  other  variety  of  Agate  known 
as  Vein  Agate  is  rather  different  in  origin  and  will  be 
referred  to  later. 

It  will  thus  be  seen  that  the  Agates  have  their  shape 
determined  by  that  of  the  cavity  in  which  they  are  formed, 
that  they  are  of  newer  formation  than  the  rocks  in  which 
they  occur,  and  that  they  are  inorganic  in  origin.  They 
consist  essentially  of  innumerable  fine  bands  of  silica  in 
one  form  or  another,  of  which  bands  the  outer  are  the  first 
formed  normally ;  the  bands  are  of  extraordinary  thinness, 
and  Sir  D.  Brewster,  who  carefully  measured  them,  stated 
they  varied  from  TY^O  t°  s^eu  °f  an  mcn  '»  ^nus  Agate  in  a 


166  PRECIOUS   STONES. 

thin  section  across  the  bands  acts  as  a  diffraction  grating 
when  held  to  the  light,  and  produces  a  spectrum. 

The  Agate  is  mentioned  by  both  Theophrastus  and  Pliny, 
though  "Achates"  included  many  other  substances  besides 
this.  They  were  used  very  largely  by  the  Greeks  for 
intagli,  and  by  the  Eomans  for  their  supposed  medicinal 
virtues. 

Although  Agates,  as  known  cut,  are  of  such  various 
colours,  many  of  these  colours  are  due  to  natural  changes, 
after  formation,  and  still  more  to  unnatural  staining  by  the 
cutter  of  the  Agate.  As  already  stated,  Chalcedony  is 
either  colourless  or  is  tinted  with  grey,  which  may,  in  thick 
pieces,  appear  a  slate-grey  to  blue-grey ;  this  gives  the 
predominant  tint  to  an  unweathered  Agate.  The  presence 
of  disseminated  zeolitic  material  in  those  parts  known  as 
Cach along  bands  produces  various  soft  tints  of  cream  and 
lavender  colour.  The  outermost  part  of  all  is  coloured  by 
Saponite,  to  a  dull  green,  and  the  whole  Agate  may  have 
its  Chalcedony  so  mixed  with  Saponite  or  Celadonite  that  its 
colour  may  be  deep  green.  More  rarely  an  iron  compound 
(probably  in  the  ferrous  condition)  is  carried  in,  and  on  oxida- 
tion yields  either  the  red  oxide  of  iron  Haematite,  or  the  yellow 
hydrate  Limonite,  with  the  formation  of  bands  of  Jasper  of 
these  colours.  Where  the  ferric  oxide  has  separated  as 
minute  spheroids,  the  colour  is  a  transparent  one  instead 
of  opaque,  and  then  the  Agate  is  termed  Carnelian  Agate. 
Other  Agates  show  a  later  infiltration  by  iron  salts  with 
the  deposition  of  Haematite  in  certain  bands  only,  for  once 
formed,  some  bands  hardly  absorb  any  such  solution  at  all ; 
such  specimens  have  quite  a  distinct  appearance  from  the 
Carnelian  Agates.  Another  later  change  which  may  affect 


PEECIOUS   STONES.  167 

the  colour  is  the  segregation  of  the  zeolitic  matter  in  the 
Cachalong  bands,  which  has  the  effect  of  leaving  these 
bands  quite  translucent  in  part  or  in  whole.  Again,  the 
Opal  bands,  which  seem  to  have  a  tendency  to  lose  their 
water,  may  have  passed  into  ordinary  Chalcedony,  only 
showing  their  original  character  by  their  evidence  of 
deposition  under  the  influence  of  gravity  alone,  surface 
tension  not  having  affected  them  apparently.  Still  further 
forms  of  colouring  are  due  to  weathering  of  the  Agates,  and, 
as  one  might  expect,  the  change  is  seen  to  occur  first  on  the 
outer,  or  older,  layers  of  the  Agate,  since  they  are  most 
exposed ;  the  commonest  change  is  for  a  red  coloured  Agate 
to  be  bleached  to  a  chalky  white,  either  throughout  or  on 
the  outermost  layers.  Cracks  are  found  developed  from  the 
same  exposure,  and  through  these  arises  another  form  of 
Agate  known  as  Mocha,  by  the  infiltration  along  the 
cracks  of  solutions  of  manganese,  and  the  deposit  within  the 
cracks  of  Pyrolusite  in  dendritic  forms.  In  some  cases,  the 
whole  of  the  Agate  within  the  "  skin,"  or  perhaps  only  the 
most  recently  formed  part,  may  be  filled  with  crystalline  or 
even  crystallised  Quartz,  either  as  Rock  Crystal,  Smoky 
Quartz,  or  Amethyst,  thus  giving  a  colourless,  a  smoky  or 
a  violet  interior  to  the  stone ;  the  Agate  in  such  a  case  may 
consist  of  anything  from  a  mere  hollow  shell  to  a  solid 
mass.  The  Quartz  in  these  instances  may  contain  needles 
or  scales  of  Gothite ;  more  rarely  the  interior  of  the 
Agate  may  be  pink  from  the  presence  of  Dolomite. 

The  lustre  varies  with  that  of  the  different  constituents, 
as  do  the  diaphaneity  and  other  physical  characters. 

The  origin  of   Agate   has    been    considered    in    dealing 
with  the  origin  of  precious  stones  in  general. 


168  PKECIOUS  STONES. 

Of  the  shape  of  Agates  it  must  suffice  to  say  it  follows 
that  of  the  containing  steam  cavity ;  if  this  cavity  were 
formed  in  a  stationary  viscid  mass  of  rock  it  would  have 
much  the  form  of  a  bubble  of  air  slowly  rising  through 
glycerine ;  this  common  form  may  be  called  balloon- 
shaped.  Where  the  lava  stream  has  been  slowly  moving 
at  the  time  the  cavity  was  formed  the  cavity  becomes 
drawn  out  just  as  our  imaginary  air  bubble  would  if  the 
glycerine  were  slowly  poured  on  a  cold  day  from  one  vessel 
to  another  :  it  is  lenticular  or  almond-shaped,  and  hence 
such  cavities  are  called  amydaloidal  cavities.  Two  cavities 
may  coalesce  just  as  solidification  is  proceeding,  and  in  this 
case  an  Agate  having  a  compressed  dumb-bell  shape  may 
be  found.  Or  again  a  slight  faulting  may  occur  after  con- 
solidation before  the  filling  of  the  cavity,  resulting  in  the 
dislocation  being  apparent  in  the  Agate.  All  these  points 
help  in  the  field  to  determine  an  Agate  amongst  a  mass  of 
other  generally  rounded  stones.  The  size  of  the  cavities 
varies  from  a  microscopic  one  to  one  of  many  feet  in 
diameter. 

The  varieties  of  Agate  have  already  been  indicated  for 
the  most  part,  but  it  may  be  well  to  summarise  them. 

The  commonest  form  is  the  Banded,  and  this  when  the 
bands  are  nearly  circular  is  called  the  Ring  Agate.  If  the 
bands  are  well  marked,  narrow  and  fairly  straight,  it  is  a 
Ribbon  Agate,  though  this  term  is  frequently  applied  to  a 
certain  kind  of  Vein  Agate  too.  Onyx  Agate  owes  its 
character  to  the  opaline  bands  causing  a  parallel  arrange- 
ment of  the  layers,  the  straight-banding  being  the  charac- 
teristic point  of  Onyx.  Stalactitic  Agates  show  stalactites 
hanging  down  from  what  was  the  roof  or  dome  of  the  cavity. 


PEECIOUS  STONES.  169 

In  some  cases  the  stalactites  are  free,  in  others  they  have  at 
a  later  stage  in  growth  been  surrounded  by  Chalcedony,  and 
in  this  case  surface  tension  has  caused  the  bands  to  be 
thicker  in  the  proximity  of  the  stalactite.  Eyed  Agates,  by 
the  increased  surface  afforded  by  minute  tufts  of  other 
minerals  (often  zeolitic),  have  had  an  increased  growth  of 
Chalcedony  at  certain  points  until  the  layers  have  formed 
small  spheroidal  outgrowths,  and  these  spheroids  on  sections 
give  the  appearance  of  an  eye.  Fortification  Agates  are 
those  which  through  numerous  "  eyes "  have  had  their 
bands  formed  with  sharp  salient  and  re-entrant  angles. 
Moss  Agates  owe  their  character  to  an  early  bursting  in  of 
the  Saponite  layer  in  moss-like  fragments.  Mocha  Stones 
show  dendrites  of  Pyrolusite  along  the  cracks  caused  by 
weathering.  Jasper  Agates  have  Haematite  or  Limonite  in 
a  finely  divided  state  enclosed  in  them,  causing  opacity 
with  a  red  or  yellow  colour.  Carnelian  Agates  have 
Haematite  enclosures  in  disseminated  spherules.  Red 
Banded  Agates  are  ordinary  Agates  in  which  the  absorbent 
bands  have  been  coloured  red  by  a  subsequent  natural 
staining  by  Haematite.  Bleached  Agates  are  any  of  those 
containing  oxide  of  iron  or  zeolitic  matter  which  by  sub- 
sequent change  is  partly  decolorised  or  removed.  The 
Cloud  Agates  are  those  in  which  the  removal  of  the  zeolitic 
matter  has  been  irregular,  so  as  to  give  a  cloud-like  effect. 

The  distribution  of  Agates  is  very  wide,  but  some  localities 
are  of  outstanding  interest.  Thus  for  long  the  chief  supply 
of  cut  Agate  came  from  Prussia,  being  not  only  found  there 
but  cut  there  also.  Thus  at  Birkenfeld  in  Oldenberg, 
Galgenberg  near  Idar,  and  Struth  near  Oberstein,  the 
material  was  found  in  large  quantities  in  the  amygdaloid 


170  PEECIOUS   STONES. 

volcanic  rocks,  and  it  was  cut  at  Idar  and  Oberstein.  As 
these  stores  became  exhausted,  fresh  deposits  discovered  in 
Brazil  were  drawn  upon  ;  these  occur  in  similar  rock  in  a 
mountain  range  running  between  the  coast  in  the  southern 
part  of  Brazil  (Kio  Grande  do  Sul)  and  the  Uruguay  river 
in  Uruguay.  North  of  the  Jacuhy,  Carnelian  is  found  in 
the  beds  of  its  tributaries,  and  Agate  on  the  mountains 
around,  while  in  the  plains  to  the  south,  Onyx  with  alter- 
nate red  and  white  bands  (Sardonyx)  is  found  in  large 
masses.  Unweathered  Agate  is  found  in  the  western  part 
of  the  district  in  Uruguay. 

In  India,  Agate  is  abundantly  found  in  the  Deccan  rocks 
in  the  Kathiawar  Peninsular  to  the  west  of  the  Gulf  of 
Cambay,  and  is  largely  cut  at  Cambay  (Kambayat).  Also 
in  Eajpipla,  and  in  the  Eajmahal  Hills. 

Minor  localities  are  Jeschkenberg  and  other  places  in 
Bohemia,  in  Sardinia,  Sicily,  Arabia  and  Surinam.  The 
Scottish  localities  are  numerous,  and  though  the  Agates 
found  are  usually  not  large,  they  are  remarkable  for  their 
variety  and  beauty  ;  the  principal  ones  are  Montrose,  Glen 
Farg,  and  near  Cupar,  all  in  lavas  of  Middle  Old  Red  Sand- 
stone age ;  a  magnificent  collection  of  specimens  from 
Scottish  localities  is  in  the  Eoyal  Scottish  Museum. 

The  Applications  of  Agate. — There  are  many  purposes 
besides  those  of  ornament  to  which  this  material  is  put ;  such 
are,  its  use  for  the  knife-edges  of  chemical  balances,  for  the 
pivots  for  marine  compasses,  in  the  manufacture  of  pestles 
and  mortars  for  grinding  hard  substances,  for  burnishing 
metals,  rollers  for  use  in  textile  industries,  dies  for  moulding 
plumbago  for  lead  pencils,  etc.  But  by  far  the  greater  part 
produced  is  wrought  into  vases,  bowls,  paper-knives,  trays, 


PEEC1OUS  STONES.  171 

signet  rings,  seals,  brooches,  beads,  sleeve  links,  and  other 
such  articles.  Most  of  this  work  is  carried  on  at  Ober- 
stein,  to  which  the  Agate  is  now  taken  from  Brazil  and 
other  places,  and  from  which  it  is  sent  to  all  parts  of  the 
world.  Damon  records  the  curious  case  arising  through 
the  demand  in  Egypt  for  objects  made  of  Agate,  visitors 
liking  to  take  away  this  "local  product"  as  a  souvenir. 
What  they  buy  would  seem  to  be  Brazilian  Agate  worked  at 
Oberstein.  We  need  not  go  out  of  England  for  similar 
instances.  Cumberland  being  a  county  justly  noted  for  its 
variety  of  minerals  is  expected  to  produce  Agate;  hence  in 
some  of  its  tourist  towns  one  sees  large  quantities  of  gor- 
geously stained  Agate  which  in  all  probability  came  from 
Brazil  in  the  first  instance,  and  Oberstein  in  the  second. 
Another  curious  case  is  the  exportation  to  Central  Africa 
from  Oberstein  of  a  large  quantity  of  Agate  cut  and  polished 
in  cylindrical  forms,  to  be  sold  as  charms. 

Many  very  beautiful  works  of  art  have  been  produced  in 
this  material.  France  possesses  a  complete  service  in  Agate, 
valued  at  one  time  at  ^20,000 ;  and  many  fine  examples  of 
this  work  are  to  be  seen  in  most  of  our  larger  museums. 

Before  the  Agate  is  cut  it  undergoes  some  important 
processes  of  preparation  in  many  cases ;  these  consist 
chiefly  in  staining  the  material  different  colours ;  the 
staining  depends  on  the  various  layers  having  different 
porosities.  Probably  the  earliest  kind  of  staining  known 
was  the  black,  which  seems  to  have  been  first  practised  in 
Italy ;  it  is  produced  by  soaking  the  material  in  some  car- 
bonaceous matter,  sometimes  an  oil,  more  often  a  solution 
of  sugar  or  honey ;  the  material  is  placed  in  vats,  covered 
by  the  solution,  and  the  whole  kept  at  a  temperature  a 


172  PEECIOUS  STONES. 

little  below  boiling  point  for  a  time,  varying  from  a  few 
hours  in  the  "  softer  "  (or  more  absorbent)  varieties  such 
as  the  Brazilian,  to  a  week  or  more  in  the  case  of  the 
"harder"  kinds.  After  being  washed,  the  Agate  is  next 
placed  in  sulphuric  acid,  which  dehydrates  the  sugar ;  this 
results  in  a  fine  black  deposit  being  left  in  the  pores  of  the 
absorbent  bands.  Staining  is  said  to  proceed  more  rapidly 
in  radial  directions.  Much  of  the  material  so  treated  is 
not  true  Onyx  in  the  mineralogical  sense,  but  Agate,  having 
alternate  bands  of  Cachalong  and  Chalcedony  ;  but  where 
the  bands  are  uniform,  and  capable  of  taking  a  good  stain, 
it  is  known  under  the  trade  name  of  Onyx. 

Another  well-known  method  of  staining  is  by  treating  the 
material  in  hydrochloric  acid  at  a  moderate  temperature 
for  about  two  weeks,  when  many  of  the  bands  assume  a 
rich  lemon-yellow  colour. 

Agate  may  also  be  made  to  resemble  a  Carnelian  Agate 
by  allowing  a  solution  of  ferrous  sulphate  to  soak  into  the 
absorbing  bands ;  this,  on  heating,  oxidises  to  ferric  oxide, 
and  gives  the  well-known  carnelian-pink. 

Green  is  produced  by  treatment  with  chromic  acid  and 
subsequent  heating,  and  an  apple-green  tint  may  be  induced 
by  soaking  in  a  solution  of  a  green  nickel  salt. 

Blue  of  various  shades  is  imparted  by  treating  first  with 
a  solution  of  potassium  ferro-cyanide,  and  afterwards  by  a 
warm  solution  of  ferrous  sulphate.  The  tint  varies  from 
indigo  to  azure  and  ultramarine. 

Many  of  the  methods,  however,  are  kept  as  strict  trade 
secrets,  but  other  methods,  as  the  use  of  aniline  dyes  and 
the  induction  of  coloured  chemical  precipitates  by  double 
decomposition,  will  suggest  themselves  to  the  reader, 


PEEOIOUS   STONES.  173 

The  staining  is  chiefly  carried  out  at  Idar  and  Oberstein, 
where  also  the  cutting  is  performed.  The  apparatus 
formerly  used  in  cutting — or  more  properly,  grinding — 
was  a  large  grindstone,  about  4  feet  in  diameter,  and  1  foot 
thick,  driven  by  a  water-wheel,  the  streams  in  the  neighbour- 
hood affording  a  plentiful  supply  of  cheap  power  for  the 
purpose.  At  Oberstein  practically  the  whole  population  is 
engaged  in  this  work.  The  grindstones  are  fixed  on  a 
horizontal  axis,  slightly  above  the  floor  level,  and  the 
grinders  lie  on  their  chests  at  full  length,  supported  on  a 
low  rest ;  the  Agate  is  held  on  a  level  with  the  axle  of  the 
wheel,  and  pressed  against  it ;  the  wheel  turns  at  about 
180  revolutions  per  minute,  so  that  a  peripheral  velocity,  or 
cutting  speed,  of  about  2,000  feet  per  minute  is  obtained  ; 
in  skilful  hands,  this  enables  the  work  to  be  done  at  a  much 
greater  rate  than  one  would  expect.  The  grindstones  are 
provided  with  grooves  of  different  curvatures,  so  that  a 
large  number  of  pieces  can  be  ground  to  a  similar  form 
with  rapidity.  Although  the  wheels  are  kept  wet,  the 
occupation  is  a  dangerous  one  to  the  health.  At  Birken- 
feld,  also  on  the  Nahe,  the  worker  usually  owns  his  own 
machinery,  or  it  is  held  in  a  small  partnership,  represent- 
ing about  £100  capital,  and  there  a  good  worker  can  earn  £3 
to  £5  per  week.  Now  most  of  the  works  at  Oberstein  are 
fitted  with  more  modern  machinery,  including  grinding  discs 
rotating  in  a  horizontal  plane.  The  polishing  is  performed 
by  women,  and  even  children,  on  smaller  wheels  of  softer 
material  dressed  with  a  mixture  of  tripolite  and  water. 

The  value  of  the  rough  material  varies,  according  to  its 
suitability  for  staining,  from  £5  to  £250  per  hundredweight 
(Max  Bauer). 


174  PRECIOUS   STONES. 

Vein  Agates  are  similar  in  composition  to  the  true  Agates, 
but  they  are  found  in  more  or  less  elongated  fissures  in  the 
rocks  instead  of  iruclosed  spaces ;  hence  they  are  more 
prone  to  contain  sufficient  foreign  matter  to  render  them 
opaque. 

The  two  chief  varieties  are  the  Eibbon  Agate,  in 
which  the  bands  are  arranged  nearly  parallel,  and  the 
Brecciated  Agate  ;  the  latter  is  of  interest  in  indicating 
movement  in  the  fault,  in  which  it  has  been  formed,  after 
partial  filling  of  the  space  with  silicious  material,  and  then 
a  uniting  of  the  broken  fragments  into  a  solid  mass  by  a 
further  deposition  of  silica.  The  former  kind  is  found  in 
Saxony  at  Schlottwitz  and  Halsbach,  and  the  latter  at 
Altendorf,  besides  in  many  less  important  localities  in  other 
parts. 

The  varieties  7,  Onyx ;  8,  Sardonyx ;  and  9,  Jasper 
Agate,  have  been  dealt  with  above. 

10.  Silicious  Sin.ter  is  a  cellular  form  of  Quartz  which 
has  been  deposited  by  uprising  heated  waters. 

11.  Flint,  formed  by  the  deposition  of  compact  silica  by 
downward  percolating  water,  often  around  organic  remains, 
does  not  concern  us  in  the  present  relation. 

12.  Hornstone  is  a  compact  brittle  form  of  silica,  with  a 
splintery  fracture,  slightly  translucent. 

13.  Lydian  Stone,  or  Touchstone,  is  a  shale  which  has 
been  altered  by  heat  in  the  vicinity  of  masses  of  intrusive 
rock  ;  it  sometimes  shows  rather  pretty  banding  of  greens 
and  browns,  but  is  very  rarely  cut  and  polished. 

14.  Jasper  includes  the  opaque,  compact  varieties  of  silica, 
coloured  by  various  impurities.     It  is  of  various  colours, 
according   to  the  impurities   present ;    thus  disseminated 


PEECIOUS   STONES.  175 

ferric  oxide  gives  a  bright  red;  the  hydrated  oxide  of  iron, 
Limonite,  imparts  various  shades  of  yellow.  Some  of  the 
minerals  allied  to  Chlorite  and  Sapo^nite  impart  a  dark 
leek  green ;  more  rarely  a  grey- blue  is  seen,  or  black.  It 
has  a  dull  lustre  and  a  large  conchoidal  fracture.  The 
impurities  may  amount  to  as  much  as  20  per  cent,  of  the 
substance.  What  has  been  said  of  the  origin,  application, 
and  cutting  of  Agate  applies  to  Jasper  in  most  cases,  only 
two  special  kinds  demanding  further  notice. 

Egyptian  Jasper  is  a  form  occurring  in  nodules  in  the 
Egyptian  deserts  and  showing  the  characteristic  surface 
erosion  caused -by  blown  sand.  The  nodules  are  derived 
from  the  nummulite  rocks,  and  are  of  a  general  brownish 
colour,  showing  concentric  markings  outlined  in  various 
shades  of  brown  and  yellow. 

Wood  Jasper  is  a  fossil  wood  silicified.  On  polishing,  all 
the  structure  of  the  wood  is  well  seen.  It  may  occur  with 
the  silica  in  a  colourless  form,  when  it  would  be  more 
rightly  classed  with  Chalcedony  or  Quartz.  It  is  not  often 
used  now  for  ornament,  except  perhaps  for  inlaying  work, 
but  it  was  used  in  ancient  times  much  more.  It  is  found 
at  Chalcedony  Park,  Arizona,  and  Yellowstone  Park,  in 
North  America. 

The  localities  where  Jasper  is  found  are  numerous  and 
widely  distributed.  Many  very  beautiful  varieties  are 
found  in  Scotland,  chiefly  in  association  with  the  Old  Eed 
Kocks,  as  in  the  neighbourhood  of  Edinburgh,  in  the 
Garleton  Hills,  and  at  Burn  Anne,  near  Galston.  Ked 
Jaspers  are  largely  obtained  from  various  parts  of  Ger- 
many, yellow  from  Sicily,  green  from  the  Urals,  and  blue 
from  Bohemia. 


176  PEECIOUS   STONES. 

Further  information  about  these  interesting  and  often 
beautiful  forms  of  silica  will  be  found  in  Mr.  Kudler's 
article  on  "  Agates  and  Agate  Cutting "  (Popular  Science 
Review,  Vol.  I.) ;  and  in  the  article  on  "  Agates,  Carnelians, 
and  Jaspers  "  ("  Trans.  Scot.  Nat.  Hist.  Society,"  Vol.  I.)  ; 
and  the  "  Guide  to  the  Collection  of  Scottish  Agates " 
(H.M.  Stationery  Office),  both  by  the  late  J.  G.  Goodchild, 
of  H.M.  Geological  Survey. 

212.  OPAL. 

Opal  is  a  mineral  of  very  similar  composition  to  Quartz, 
yet  its  whole  character  differs  from  that  of  Quartz  in  a 
marked  way.  It  was  known  in  ancient  times,  and  Pliny 
gives  as  good  (and  as  often  quoted)  a  description  of  it  as 
can  be  worded.  The  great  value  set  by  the  Komans  on  the 
gem  may  be  gathered  from  Pliny's  account  of  the  Opal 
belonging  to  Nonius,  who  was  proscribed  in  the  hopes  of 
making  him  give  up  his  gem  to  the  Triumvir.  Kather 
than  do  this  he  fled.  His  gem  was  valued  at  what 
would  now  be  £20,000,  and  yet  it  was  no  larger  than  a 
hazel-nut  (King). 

It  is  a  stone  that  has  always  been  surrounded  in  the 
popular  mind  with  a  mass  of  superstitions.  In  early  times 
it  was  held  to  be  a  protection  to  the  sight.  This  seemingly 
led  Marbodus  to  alter  the  name  of  it  to  Ophthalmius,  and  at 
the  same  time  to  endow  it  with  the  further  virtue  of  render- 
ing the  wearer  invisible.  Thus  at  this  time  it  was  rather  a 
"  lucky  "  stone.  Now  it  remains  as  one  of  the  few  stones  to 
which  one  hears  superstitions  attached ;  but  its  property 
has  mysteriously  changed,  and  it  is  not  unknown  to  hear 
"  Oh !  I  never  wear  Opals,  they  are  so  unlucky." 


PRECIOUS  STONES.  177 

The  outstanding  feature  of  Opal  is  its  colour — at  any  rate, 
so  far  as  the  variety  used  as  a  gem  stone  (Precious  Opal)  is 
concerned.  What  the  colour  is  due  to  has  never  been  quite 
ascertained,  though  there  is  no  doubt  it  is  an  optical  effect ; 
it  has  been  suggested  that  minute  cavities  cause  refraction 
and  reflection  (Brewster) ;  also  that  it  is  due  to  interference 
of  light  in  cracks ;  more  recently  Behrends  has  ascribed  it 
to  the  existence  of  numerous  thin  lamellae,  which  have  at 
one  time  been  parallel,  but  later  bent  and  cracked  into  a 
curved  form.  The  colours  shown  in  Precious  Opal  are 
remarkable  for  their  intensity,  and  may  be  likened  to  the 
light  emitted  by  some  of  the  double  stars,  or  to  the  colours 
seen  in  the  feathers  of  certain  birds.  Thus  brilliant  and 
pure  greens,  vivid  crimsons,  electric-blue  are  seen,  with  often 
a  dominant  soft  blue ;  sometimes  a  rich  violet  or  a 
sherry  yellow  appear,  very  rarely  rose-red  and  black. 
Owing  to  the  substance  being  sub-transparent,  and  of  a 
pale  amber  colour  by  transmitted  light,  an  Opal  often  shows 
a  blending  of  this  yellow  light  transmitted  through  the 
stone  with  the  optical  colours,  giving  an  appearance  known 
as  "  opalescence."  Other  varieties  of  Opal  may  show 
different  colours,  as  white,  yellow,  brown,  grey,  green,  etc., 
quite  apart  from  any  play  of  colour. 

The  lustre  varies  from  vitreous  to  resinous,  or  rarely 
pearly ;  sub-transparent  to  opaque. 

Refraction  is  normally  single,  nr  =  1*442 — 1*446  ;  but 
anomalous  double  refraction  is  sometimes  seen  through 
internal  strain. 

The  specific  gravity  is  1'9 — 2*3,  purer  forms  about  2*19 — 
2*2.  It  has  a  conchoidal  fracture,  and  gives  a  white  streak. 

It    is    always   amorphous,    and  occurs   in    reniform    or 

p.s.  K 


178  PKECIOUS  STONES. 

stalactitic  masses.  Precious  Opal  more  often  is  found 
mixed  with  matrix  and  forming  disseminated  patches  and 
veins. 

The  hardness  is  5'5  to  6'5. 

The  origin  seems  very  similar  to  that  of  many  other 
forms  of  silica — deposition  in  cracks  and  cavities  in  rock 
from  watery  solutions  of  silica,  usually  percolating  down- 
wards, as  described  previously.  It  is  usually  met  with  in 
decomposing  volcanic  rocks,  but  may  be  found  in  any  silica 
containing  rock.  It  is  associated  with  Quartz,  Chalcedony, 
and  other  modifications  of  silica  as  a  rule. 

In  chemical  composition  it  is  a  hydrated  oxide  of  silicon, 
Si02,  nH20,  the  amount  of  water  varying,  so  that  one  may 
almost  say  there  is  a  transition  from  Opal  to  Chalcedony. 
The  water  percentage  varies  from  0*1  to  lO'O  per  cent,  or 
more.  Heating  drives  off  this  water  and  ruins  the  gem. 

Varieties : — 

1.  Precious  Opal — that  showing  the  fine  play  of  colour 
described  above.  According  to  the  form  in  which  the 
colour  appears  (the  "pattern"  of  the  Opal),  it  is  subdivided 
into 

a.  Harlequin  Opal  ,that   in  which  the  light  appears  in 

small  angular  patches  ; 

b.  Pin  Point  Opal,  in  which  the  points  of  light  are  very 

minute  ; 

c.  Flame  Opal,  with  the  colour  in  streaks ; 

d.  Gold  Opal,  showing   a  yellowish  light  over  a  large 

area 

Precious  Opal  in  Plinv's  time  came  solely  from  India, 
though  none  is  known  from  that  country  now.  Even 
early  in  the  seventeenth  century  India  still  produced  the 


PRECIOUS   STONES.  179 

best  stones,  though  the  Hungarian  locality  was  known. 
It  is  very  likely  that  many  of  the  supposed  Indian  specimens 
were  Hungarian  ones  that  found  their  way  to  the  West  from 
Constantinople. 

The  Hungarian  locality  is  at  Czerwenitza,  near  Eperies 
(Presova),  in  Saros.  The  Precious  Opal  here  occurs  in 
fissures  in  a  weathered  andesitic  lava  with  other  forms  of 
Opal ;  it  was  formerly  quarried  in  open  workings,  but  now 
a  perfect  network  of  levels  has  burrowed  into  the  mountain. 
The  largest  mass  found  here  is  in  the  Imperial  collection  at 
Vienna  ;  it  weighs  about  3,000  carats,  and  is  of  the  size  of 
a  man's  fist.  When  the  Opal  is  in  small  disseminated 
patches  in  the  matrix,  the  whole  is  sometimes  cut  and 
mounted  together,  the  matrix  being  oiled  to  darken  it. 
Such  material  is  known  as  "  Mother-of-Opal."  Cutting  the 
Precious  Opal  is  a  very  delicate  operation  on  account  of  the 
liability  to  breakage  of  the  gem  from  the  numerous  flaws. 
It  is  partly  cut  in  Hungary,  the  operators  using  a  leaden 
disc,  with  emery  as  an  abrasive.  The  form  of  cutting 
employed  is  nearly  always  one  with  a  low  curved  upper 
surface  without  any  facets. 

These  mines  have  certainly  been  known  from  the  four- 
teenth century.  Hungarian  Opals  show  the  finest  fire,  and 
their  colours  deteriorate  least  with  exposure. 

Precious  Opal  is  also  found  in  a  weathered  volcanic  rock 
in  the  west  of  Honduras,  where  it  occurs,  as  in  Hungary,  as 
patches  in  common  Opal. 

In  Mexico  it  occurs  in  the  State  of  Queretaro,  north-west 
of  the  city  of  Mexico,  in  volcanic  rock,  and  associated  with 
other  forms  of  Opal.  The  colours  are  often  intense,  but  in 
larger  patches  than  the  Hungarian  specimens  show,  and 

N2 


180  PKECIOUS   STONES. 

the  colours  do  not  change  so  much  when  the  stone  is  moved. 
The  sub-variety,  Lechosos-Opal,  which  occurs  here,  shows 
specks  of  emerald-green  and  carmine. 

In  New  South  Wales,  in  a  decomposed  amygdaloidal 
volcanic  rock,  Precious  Opal  occurs,  associated  with  other 
forms  of  Opal ;  this  is  at  Kocky  Bridge  Creek,  in  Georgina 
County.  Also  at  White  Cliffs,  Yungnulgra  County,  there  is  a 
deposit  of  considerable  importance,  both  because  of  its 
commercial  value  and  also  on  account  of  its  peculiar 
matrix,  which  is  a  white  sandstone.  The  Precious  Opal, 
along  with  common  Opal,  occurs  in  the  joint-  and  bedding- 
planes  of  the  rock.  Cretaceous  fossils  are  found  in  some 
cases  filled  with  Precious  Opal,  and  fetch  very  high  prices 
as  curiosities;  it  also  is  found  pseudo-morphous  after 
Gypsum  (E.  F.  Pittman). 

In  Queensland,  at  Bulla  Creek,  Precious  Opal  again  is 
found  in  a  silicious  rock,  in  this  instance  a  highly  fer- 
ruginous sandstone,  in  the  fissures  of  which  it  occurs  in 
thin  layers  in  association  with  common  Opal.  The  colour  of 
this  Opal  is  of  a  deep  blue  in  general,  with  large  areas  of  the 
same  shade  nearly  ;  it  of  course  has  the  green  and  red  "  fire." 

2.  Fire  Opal  is  of  a  reddish  tint  from  the  presence  of 
ferric  oxide,  but  it  may  show  the  same  play  of  colour  as 
Precious  Opal.     The  name  refers  to  its  red  colour,  and  on 
the  same  account  it  is  sometimes  called  Sun  Opal.     It  is 
particularly  liable  to  deteriorate  through  exposure.     It  is 
found  usually  associated  with  other  varieties  at  Zimapan  in 
Mexico,  in  Honduras,  and  in  the  Faroe  Islands. 

3.  Girasol  is  a  bluish  white  variety  with  a  rather  feeble 
red  "fire";    on  moving  the  stone  a  faint  wave  of  bluish 
light  may  be  seen  to  move  across  it.     It  is  found  in  the 


pttEdotJs  STONES.  isi 

Faroes,  and  rarely  in    Scotland   at    Usan.     Fire   Opal   is 
sometimes  called  Girasol  also. 

4.  Common  Opal  includes  a  considerable  number  of  sub- 
varieties.     In  one  form  or  another  it  is  very  common,  large 
masses  of  hydrous  silica  occurring  in  some  parts.     As  in 
the  case  of  Chalcedony,  the  pure  kinds  are  translucent  and 
colourless,  but  with  the  addition  of  various  impurities  many 
varying  forms  arise.      Milk  Opal  shows  white,  bluish,  or 
greenish  tints.     Resin  Opal,  or  Pechopal,  has  a  resinous 
lustre  and  a  yellow  colour.     Semiopal  is  a  sub-translucent 
kind.     Hydrophane    is  a  light   coloured  variety,  which  is 
absorbent  enough  to  adhere  slightly  to  the  moistened  finger, 
and  it  has  the  property  of  becoming  more  translucent  when 
placed  in  water,  hence  the  name. 

The  more  massive  forms  of  Common  Opal  are  ground 
and  polished  for  much  the  same  purposes  as  Agate  is, 
e.g.,  pin  trays,  knobs  for  umbrellas,  sleeve-links.  Common 
Opal  is  found  in  all  the  localities  mentioned  under  Precious 
Opal,  also  in  Moravia  and  Bohemia,  at  Kosemtitz  in  Silesia, 
in  Iceland,  Ireland,  Scotland. 

5.  Cacholong  Opal  is  very  feebly  translucent  from  the 
presence  of    disseminated  mineral  matter,  which  is  often 
zeolitic.      It   is   often    present  in   Agate   alternating  with 
Chalcedony,  and  such  banded  specimens  may  be  used  for 
cameo-cutting.      The  Faroe  Islands  may  be  instanced  as 
producing  very  fine  specimens. 

6.  Opal  Agate  is  more  correctly  included  under  Agate. 

7.  Menilite  is  a  concretionary  form  found  at  Menilmontane, 
near  Paris,  embedded  in  a  clayey  shale.    It  is  brown  or  grey 
in  colour,  and  sometimes  shows  alternate  bands  of  these  two 
colours. 


182  PRECIOUS  STONES. 

8.  Jasp-Opal   is   a  form   containing    sufficient    diffused 
impurity  (often  an  iron  compound)  to  render  it  opaque. 

9.  Wood  Opal   consists  of    the  fossil  remains  of  wood 
infiltrated  with  hydrous  silica.     When  cut  and  polished  it 
shows  all  the  detailed  structure  of  the  wood  very  clearly. 
It  is  found  near  Hobart  Town  in  Tasmania,  Kremnitz  in 
Hungary,  and  many  other  places. 

10.  Hyalite,  or  Muller's  Glass,  is  an  absolutely  colourless 
and  usually  transparent  Opal  occurring  in  small  botryoidal 
masses  resembling  beads  of  fused  glass.     It  resists  solution 
by  alkalies  more  than  other  forms  ;  it  is  found  at  Kremnitz 
in  Hungary  and  in  Bohemia,  amongst  other  places. 

11.  Silicious   Sinter  is  a  more  porous  form,  chiefly  of 
interest  from  its  origin  in  deposition  from  uprising  heated 
water  in  fumaroles  and  hot  springs. 

The  applications  to  which  Opal  is  put  are  all  those  of 
ornament,  and  these  have  been  already  indicated.  All 
kinds  are  cut  in  thin  slices,  usually  with  a  curved  upper 
surface  (en  caboclion),  except  the  Fire  Opal,  which  may  be 
cut  in  a  deeper  form  and  facetted.  The  value  depends  very 
largely  on  the  quality  of  the  colour  and  on  the  pattern. 
The  favourite  type  is  a  Harlequin  Opal  showing  bright 
green  and  crimson  flashes ;  such  a  stone  of  one  carat 
may  fetch  over  ,£2.  More  recently  Opal  cut  in  the  matrix 
has  been  fashionable,  though  how  long  it  will  remain  so  is 
uncertain. 

Opal  is  rarely  imitated,  but  sometimes  glass  imitations 
are  mounted  with  foil  in  a  closed  setting  to  give  the  effect 
of  play  of  colour;  such  an  imitation  can  be  detected  at 
once  by  the  inferior  hardness  of  the  glass. 


CHAPTER  VIII. 

231.    CORUNDUM. 

THIS  mineral  species  includes  some  of  the  most  important 
precious  stones,  its  blue  crystalline  variety  being  the 
Sapphire  and  the  red  the  Ruby,  while  other  colours 
are  known  as  Oriental  Topaz,  Oriental  Amethyst,  etc. 
Since  these  are  all  the  same  mineral,  with  only  slight 
variations  in  the  colouring  matter,  they  will  all  be  treated 
collectively  so  far  as  possible.  To  the  old  writers  they 
were  regarded  as  of  many  species.  Thus  the  Sapphire  was 
the  Hyacinthus  of  Pliny,  and  included  his  variety  Asteria. 
The  Ruby  was  regarded  by  him  as  belonging  to  the  Lychnis 
group  of  the  Carbunculi ;  but  much  confusion  of  terms  has 
crept  in  in  the  writings  of  many  of  the  early  mineralogists. 

Dependent  on  the  colour  is  the  jeweller's  classification 
of  the  varieties ;  mineralogically  these  are  sub-varieties  of 
the  crystallised  Corundum.  The  two  most  common  kinds 
are  the  blue  Sapphire  and  the  red  Ruby ;  but,  as  indicated 
above,  a  number  of  other  colours  occur  which  are  practically 
identical  with  the  colours  of  other  well-known  gems,  and 
hence  to  distinguish  the  more  valuable  forms  of  Corundum 
the  jeweller  prefixes  the  term  "  Oriental  "  to  the  name  of 
the  gem  whose  colour  is  that  of  the  stone  in  question. 
Thus  Topaz  is  the  mineral  known  to  the  mineralogist  by 
that  name  ;  but  Oriental  Topaz  is  a  yellow  Corundum,  and 
the  opposite  term  "Occidental"  would  be  applied  to  such  a 


184  PEEOIOUS  STONES. 

less  valuable  mineral  as  yellow  Quartz — thus  "  Occidental 
Topaz."  The  red  of  the  Euby  varies  a  good  deal,  the 
"masculine"  Ruby  showing  the  deeper  tints  of  carmine  or 
blood-red  (often  referred  to  as  "  pigeon's  blood  "-red,  from 
a  Burmese  simile),  while  the  "feminine"  Ruby  is  paler, 
and  more  of  a  rose-red ;  in  this,  as  in  other  varieties  of 
Corundum,  a  transition  is  seen,  and  the  feminine  Ruby  may 
pass  gradually  to  colourless  Corundum.  The  masculine 
Ruby,  in  its  most  admired  shades,  has  a  slight  blue  tone  in 
the  red,  which  thus  tends  to  magenta.  The  colour  is 
usually  evenly  distributed  in  the  Ruby,  but  in  the  Sapphire 
it  is  quite  usual  to  find  much  variation  in  depth  of  colour. 
All  shades  of  blue  are  found  and  of  all  depths.  Perhaps  the 
most  characteristic  colours  are  a  smalt-blue  and  a  corn- 
flower blue.  Deep-coloured  stones  are  known  as  Lynx-  or 
Cat-  Sapphires,  and  the  paler  ones  as  feminine  stones  or 
Water- Sapphires,  though  the  latter  term  is  more  often 
applied  to  the  blue  lolite  (Cordierite) .  Pale  Sapphires 
merge  insensibly  into  the  next  colour  variety,  Leuco- 
Sapphire,  which  is  really  devoid  of  colour — simply  colour- 
less crystallised  Corundum.  It  also  passes  into  the  blue- 
green  variety,  known  as  Oriental  Aquamarine.  In  fact,  in 
many  crystals  of  Corundum  a  gem  might  be  cut  from  one 
end  which  would  be  a  Sapphire,  while  from  the  other  end 
of  the  crystal  a  Leuco-Sapphire  might  be  obtained.  The 
yellow-green  variety  of  the  colour  of  Chrysolite  (Olivine)  is 
called  Oriental  Chrysolite.  The  intense  green  s.tones  are 
Oriental  Emerald;  the  pure  amber,  or  honey-yellow  stones, 
are  Oriental  Topaz ;  while  those  of  a  rich  brownish-red 
are  known  as  Oriental  Hyacinth,  and  the  violet  specimens 
as  Oriental  Amethyst.  All  these  tints  are  found  in  the 


PBECIOUS  STORES.  185 

first  mineralogical  variety.  Those  kinds  which  have  a 
well-marked  crystalline  structure  but  are  of  dull  tint  and 
not  transparent  are  classed  as  the  second  variety,  common 
Corundum,  the  Adamantine  Spar  of  Black,  and  the  Adamas 
Siderites  of  Pliny.  The  more  common  colours  seen  are 
dull  blue  to  grey  and  smoke-brown  to  black.  The  third 
variety  does  not  depend  so  much  on  colour  as  on  its  less 
defined  crystalline  structure.  It  is  called  Emery,  and  is 
the  substance  so  well  known  as  a  polishing  agent ;  but 
even  in  "knife-powder"  one  may  sometimes  isolate  quite 
distinct  though  microscopic  Sapphires.  Emery  is.  usually 
granular  and  massive. 

The  lustre  of  the  purer  varieties  is  adamantine,  but  it 
passes  gradually  into  vitreous  in  the  less  pure  forms.  On 
the  basal  plane  it  is  sometimes  pearly. 

Diaphaneity.  As  indicated  above,  the  purer  forms  are 
transparent,  others  sub-transparent  to  opaque. 

It  is  doubly  refracting,  but  not  in  a  marked  degree,  the 
index  for  yellow  light  being  in  the  ordinary  ray  1*769,  and 
in  the  extraordinary  ray  1'760,  and  the  dispersion  is  slight. 
Being  doubly  refracting,  it  is  of  course  capable  of  lighting 
the  field  under  the  crossed  Nicols  of  the  polariscope.  The 
coloured  varieties  show  a  marked  dichroism,  especially  in 
specimens  having  a  deep  colour,  in  which  the  phenomenon 
may  be  so  well  marked  as  to  be  obvious  to  the  eye.  A 
Euby,  when  seen  through  the  dichroscope,  shows  one 
image  of  a  rich  red  inclining  to  violet,  while  the  other  is 
of  a  paler  red.  Sapphire  shows  images  of  a  rich  deep  blue 
and  a  pale  greenish  blue ;  Oriental  Amethyst  shows  a  rich 
violet  image,  and  a  very  pale  violet  or  colourless  one ; 
Oriental  Emerald  shows  a  blue  and  a  green  image. 


186  PKECIOUS  STONES. 

Phosphorescence  is  well  marked  in  some  specimens,  and 
is  well  seen  in  a  darkened  room  when  the  stone  is  carefully 
heated.  Fluorescence  is  seen  in  some  kinds,  as  the  Oriental 
Emerald  from  Siam. 

It  is  quite  infusible  before  the  ordinary  blowpipe.  On 
rubbing  with  a  dry  cloth  it  shows  a  surface  charge  of  positive 
electricity. 

The  specific  gravity  is  high,  varying  from  3'93  to  4*08, 
so  that  it  readily  sinks  in  a  saturated  solution  of  iodine  and 
iodoform  in  methylene  iodide. 

The  fracture  is  conchoidal  to  uneven,  and  the  mineral  is 
brittle.  Its  hardness  is  marked,  being 
excelled  amongst  minerals  by  the 
Diamond  alone.  It  is  the  Standard  9 
of  Mohs'  scale. 

True  cleavage  is  absent,  but  from  a 
lamellar  twinning  parallel  to  the  basal 
plane   and   to   the    unit    rhombohedron 
there    are    more    or    less    well   marked 
FIG.  u.-conmdum.  parting   planes   paranei   to   these   faces 

in  such  twinned  specimens,   and  this   simulates  cleavage 
closely. 

Crystalline  form.  Corundum  belongs  to  the  rhombo- 
hedral  division  of  the  hexagonal  system,  but  as  in  the  case 
of  Quartz,  the  rhombohedral  character  is  not  always  very 
apparent,  the  general  form  of  the  crystal  being  often  that 
of  a  doubly  terminated  and  rather  acute  hexagonal  pyramid, 
not  infrequently  truncated  by  a  basal  plane  (Fig.  14). 
Oscillations  of  pyramid  forms  between  the  basal  plane  and 
the  prism  faces  causes  a  characteristic  wavy  outline  in  many 
crystals,  and  in  nearly  all  cases  striations  can  be  seen  run- 


STONES.  187 

ning  parallel  to  the  meeting  of  the  base  and  prism.  Another 
common  habit  of  Corundum  is  a  stout  hexagonal  prism 
terminated  by  the  basal  plane ;  this  type  is  often  met  with 
in  Euby,  in  which  also  the  rhombohedral  habit  is  seen  most 
frequently. 

Chemical  composition.  Corundum  is  pure  alumina, 
A1203,  the  oxide  of  Aluminium.  Traces  of  ferric  oxide,  silica" 
and  oxide  of  chromium  are  found  in  even  the  purer  varieties 
often,  and  it  is  supposed  (though  it  is  by  no  means  certain) 
that  these  substances,  slightly  varying  in  amount  and  pro- 
portion, give  to  the  Euby,  the  Sapphire,  and  the  other 
precious  forms  of  Corundum  their  beautiful  colours  on 
which  the  value  so  largely  depends.  The  less  pure  forms 
of  Corundum  contain  large  amounts  of  iron,  especially  as 
Magnetite  and  Haematite. 

The  different  forms  of  Corundum  do  not  behave  alike 
under  the  influence  of  heat.  Thus  a  Euby  after  being 
heated  retains  its  colour,  hence  the  colour  certainly  is  not 
organic  in  nature ;  Sapphire,  on  the  other  hand,  has  its 
colour  discharged  in  the  majority  of  cases  by  heating,  and 
from  this  it  has  been  suggested  that  organic  matter  may 
account  for  the  beautiful  blue.  However,  the  prevailing 
opinion  is  that  both  owe  their  beauty  to  small  quanti- 
ties of  chromium  and  possibly  of  iron  also.  Euby  may 
with  care  be  heated  to  very  high  temperatures ;  it  turns 
a  dirty  grey  colour  when  very  hot,  but  on  cooling  it 
again  turns  to  red,  passing  through  white  and  green  as 
it  cools. 

In  considering  the  origin  of  these  gems,  it  may  be  well  to 
deal  with  their  distribution  at  the  same  time,  merely  noticing 
in  passing  that  Corundum  seems  in  the  great  majority  of 


188  PREOlOtJS  STONES. 

cases  to  be  a  product  of  thermo-  or  dynamo-metamorphism, 
or  of  a  combination  of  both. 

EUBY. — The  most  important  Kuby  mines  are  in  Burma, 
around  Mogok  to  the  east  of  the  Irrawaddy,  and  north-north- 
east of  Mandalay,  and  specimens  from  these  mines  most 
nearly  approach  the  ideal  in  colour.  A  smaller  area  of  Ruby- 
bearing  limestone  is  found  at  Sagyin  Hills,  north  of  Man- 
dalay. Professor  Judd,  in  the  article  dealing  specially  with 
the  Ruby  of  Burma  (Brown  and  Judd,  Phil.  Trans.,  Vol. 
CLXXXVIlA.),  ascribes  the  limestone  in  which  Rubies  occur 
to  a  decomposition  of  the  lime  Felspar  contained  in  the  basic 
gneisses.  There  is  a  peculiar  feature  about  the  interrelation 
of  the  limestone  and  gneisses,  for  they  show  a  considerable 
amount  of  interbedding.  The  limestones  are  not  sharply 
marked  off  from  the  gneisses,  but  merge  gradually  into  them, 
and  Mr.  Barrington  Brown  describes  them  as  having  their 
dips  conformable  to  the  contortions  of  the  gneiss  in  all 
cases.  Dr.  Noetling,  of  the  Indian  Survey,  regards  the 
igneous  rocks  as  having  been  intruded  into  the  limestone  in  a 
molten  state,  and  holds  that  the  Rubies  and  other  minerals 
contained  in  the  limestone  are  the  product  of  contact  or 
thermo-metamorphism.  The  role  played  by  heated  water 
under  pressure  would  seem  to  enable  the  formation  of  a 
gneiss  to  occur  largely  out  of  the  material  of  the  rock  around, 
and  thus  to  replace  this  rock,  the  semi-fluid  magma  at  the 
same  time  throwing  out  projections  and  enveloping  portions 
of  the  country  rock.  It  is  in  the  limestones  alone,  and  in  the 
debris  resulting  from  their  weathering,  that  the  Rubies  are 
found.  This  debris  consists  of  a  brownish  clayey  material, 
and  it  fills  the  crevices  and  "  shaks  "  of  the  limestone  and 
covers  the  sides  and  bottoms  of  many  of  the  valleys.  The 


PEEOIOUS  STONES.  189 

Burma  Eubies  show  crimson  and  aurora-red  images  in  the 
dichroscope. 

In  Siam  the  Kuby  is  found  near  the  coast  at  Krat 
and  Chantabun,  but  the  stones  are  darker  and  more  purple 
than  the  Burmese  ones.  Here  again  granitic  rocks 
and  limestone  are  found,  but  the  Euby  is  so  far  only 
known  in  the  sands  of  this  region.  Siamese  Bubies  give 
dichroscope  images  respectively  crimson  and  brownish-red. 

In  Ceylon  Buby  is  found  in  alluvial  sands  at  the  foot 
of  Adam's  Peak.  These  sands  for  the  most  part  are  found 
in  old  river  terraces ;  a  crystalline  dolomitic  limestone  is 
supposed  to  be  the  mother  rock.  The  stones  are  very  clear 
but  of  a  lighter  colour. 

In  India  Buby  occurs  but  rarely  in  good  quality,  though 
the  poorer  qualities  are  widely  distributed.  In  Afghanistan 
to  the  east  of  Kabul,  Buby  is  found  in  an  altered  lime- 
stone. 

In  the  United  States,  Buby  of  gem  quality  is  found  at 
Corvee  Creek,  a  tributary  of  the  Little  Tennessee  Biver  in 
North  Carolina,  in  a  decomposed  garnetiferous  basic  rock  ; 
many  much  weathered  specimens  have  been  found,  which 
have  led  Professor  Judd  and  Mr.  Hidden  to  conclude  that 
Bubies  of  very  large  size  have  been  formed  here  (Mm. 
Mag.,  Vol.  XII.,  p.  144). 

In  New  South  Wales  a  few  small  specimens  have  been 
found.  Also  at  several  places  in  Queensland. 

The  associated  minerals  bear  a  close  relationship  in  the 
different  localities.  In  Burma  very  fine  Spinel,  colourless 
Zircon,  Garnets,  Apatite,  different  Felspars,  Bubellite, 
Quartz,  Muscovite  and  other  Micas,  Lapis-Lazuli,  Graphite, 
Scapolite,  Pyrrhotite,  and  other  minerals  are  found,  in 


190  PBECIOUS  STONES. 

addition  to  the  Ruby,  Sapphire  and  other  gem  varieties  of 
Corundum.  In  Siam  the  associates  are  Sapphire,  Quartz, 
Ilmenite  and  Zircon.  In  Ceylon  the  gem  sands  contain, 
besides  the  Ruby,  Sapphire,  and  other  varieties  of  Corun- 
dum, Garnets,  Zircon,  Quartz,  Chrysoberyl,  Magnetite, 
Amethyst,  Tourmaline,  Spinel,  etc. 

In  North  Carolina  the  associated  minerals  are  Garnet, 
Spinel,  Monazite,  Rutile,  Ilmenite,  different  Micas,  Stauro- 
lite,  Gold,  etc.,  and  the  Rubies  often  show  inclusions 
sometimes  so  minute  as  to  give  the  gem  a  "  sheen  "  (Judd 
and  Hidden). 

The  mining  of  the  Ruby  in  Burma  is  now  carried  out  by 
the  Burma  Ruby  Mines,  Ltd.  Here  not  only  open  work- 
ings are  found,  but  also  tunnels  driven  in  to  cut  the  gem- 
bearing  material,  which  is  washed  to  free  it  from  as  much 
earthy  matter  as  possible,  the  remaining  gravel  containing 
the  Rubies  being  afterwards  picked  over  by  hand.  The 
machinery,  which  is  somewhat  similar  to  that  employed  in 
Diamond  washing,  is  now  driven  by  electricity,  transmitted 
from  some  distance. 

It  has  already  been  remarked  that  the  colour  of  a  Ruby 
varies  with  the  direction  in  which  it  is  viewed ;  the  richest 
colour  is  seen  on  looking  along  the  principal  axis  of  the 
crystal,  hence,  in  cutting,  the  gem  should  be  so  fashioned 
that  this  axis  is  presented  to  the  eye  of  the  observer,  the 
table  thus  being  parallel  to  the  basal  face  of  the  crystal. 
The  gem  is  usually  cut  as  a  brilliant.  Some  few  Rubies 
show  asterism,  and  are  cut  en  cabochon,  but  this  is  not 
nearly  so  frequently  seen  in  Ruby  as  in  Sapphire. 
More  rarely  step  cut  stones  are  seen,  or  those  in  which  the 
form  of  the  crown  is  that  of  a  brilliant,  while  the  culasse  is 


PEECIOUS  STONES.  191 

cut  in  steps.  Since  the  dispersive  power  is  small  there  is 
no  marked  play  of  colour,  and  hence  there  is  not  the  same 
importance  in  giving  the  gem  an  exact  form  as  in  the  case 
of  the  Diamond.  Hence,  too,  rose  cut  Kubies  are  relatively 
more  effective  than  rose  cut  Diamonds. 

The  grinding  is  now  usually  effected  with  Diamond  dust 
on  account  of  the  quicker  abrasion  ;  the  wheel  used  is  an 
iron  one.  Polishing  is  done  on  a  copper  disc,  dressed  with 
tripolite. 

Ruby  ranks  above  Diamond  in  point  of  value  for  good 
stones  ;  while  the  price  of  a  pale  Ruby  of  one  carat  may  only 
be  £1,  a  stone  of  rich  deep  colour,  weighing  when  cut  one 
carat,  may  fetch  £25  or  more.  Mr.  Streeter  states  that 
£20,000  has  been  paid  for  a  very  fine  Ruby  of  38T%  carats. 
While  Rubies  up  to  2,000  carats  have  been  found,  most  of 
the  larger  ones  show  considerable  imperfect  areas,  and  of 
large  flawless  Rubies  very  few  are  known  compared  to 
Diamonds  of  similar  quality  and  size. 

On  account  of  the  great  demand  for  this  rare  gem,  stones 
of  inferior  kind  are  not  infrequently  offered  as  Rubies. 
True  Rubies,  although  they  can  be  produced  artificially  (see 
"  Artificial  Production  "),  cannot  be  made  of  sufficient  size 
yet  for  gem  use,  and  moreover  the  process  is  a  very  expen- 
sive one.  The  most  common  substitutes  for  Ruby  are  the 
Balas  Ruby  (red  Spinel)  and  the  Rock  or  Elie  Ruby  (Garnet). 
Both  these  minerals  are  cubic  in  their  crystalline  form, 
hence  the  optical  properties  can  readily  be  used  to  dis- 
tinguish them,  for  they  show  no  double  refraction  and  no 
dichroism.  Their  hardness  is  in  both  cases  inferior  to  that 
of  Ruby  and  the  specific  gravity  lower.  Two  other  substi- 
tutes, however,  belong  to  the  same  crystallographic  system  ; 


192  PRECIOUS  STONES. 

these  are  Eubellite  (pink  Tourmaline)  and  red  Quartz 
("Bohemian  Kuby  ").  Here  again  the  inferior  hardness 
will  distinguish  them  from  the  Ruby  in  cases  where  one  can 
scratch  the  specimen,  and  also  the  lower  specific  gravity  as 
compared  with  Ruby.  Yellow  Topaz  which  has  been  turned 
red  by  heat  ("  Brazilian  Euby  ")  is  distinguished  by  the 
same  two  tests.  Red  Fluor  Spar,  which  is  only  very  rarely 
used  as  an  imitation  Ruby,  is  again  softer  and  less  dense. 
The  colour  of  the  Ruby  is  perhaps  most  nearly  imitated  in 
glass,  but  glass  is  singly  refracting  and  relatively  very  soft. 
Quartz  which  has  been  stained  in  cracks  can  be  recognised 
by  these  cracks,  which  can  never  be  quite  hidden  ;  it  is  called 
Rubasse. 

SAPPHIRE. — What  has  been  said  of  the  origin  and 
mode  of  occurrence  of  Ruby  applies  very  much  to 
Sapphire  too,  the  one  rarely  being  found  without  the 
other,  though  at  some  localities  one  is  more  abundant 
than  the  other. 

The  most  important  Sapphire  mines  are  in  Siam,  at 
Battambang,  but  Sapphires  are  also  found  with  the  Rubies 
in  the  mines  of  Chantabun  and  Krat.  At  Battambang  they 
occur  in  a  sandy  deposit ;  this  is  washed  and  picked  in  the 
usual  manner.  It  is  noteworthy  that  the  larger  stones  are 
usually  of  better  quality  than  the  smaller.  Gems  of  very 
fine  cornflower  blue  colour  are  obtained  from  Siam ;  they 
are  strongly  dichroic  and  show  images  respectively  blue 
and  green. 

In  the  Burma  Ruby  mines  they  are  also  found,  but  in 
much  fewer  numbers  than  are  the  Rubies,  though  the 
Sapphires  often  exceed  the  Rubies  in  size.  They  are  of 
good  quality,  faultless  stones  of  80  carats  having  been 


PRECIOUS  STONES.  193 

obtained.  Unlike  the  Siamese  Sapphires,  their  images  in 
the  dichroscope  are  blue  and  straw-colour.  They  tend  to 
be  too  dark  in  colour  in  many  cases. 

In  Ceylon  they  occur  in  the  gem  gravels  around  Adam's 
Peak  with  the  associates  mentioned  under  Euby.  Most 
of  the  Sapphires  are  found  in  the  southern  parts  of  the 
island;  they  are  supposed  to  have  been  developed  in  the 
crystalline  limestones  of  the  district,  but  as  yet  have  not 
been  found  in  situ.  The  stones  are,  like  the  accompanying 
Eubies,  very  brilliant,  but  rather  light  in  colour. 

A  more  interesting  deposit,  and  one  which  is,  in  addition, 
of  commercial  importance,  is  that  near  the  village  of 
Soomjam  in  Kashmir.  Here  in  the  early  'eighties  a  land- 
slip exposed  a  mass  of  garnetiferous  gneiss  with  interfolia- 
tions  of  an  altered  limestone  containing  granitic  veins,  and 
in  this  rock  the  Sapphires  have  been  found  in  situ  associated 
with  Tourmaline.  Most  of  the  gems,  however,  are  found 
in  detrital  matter  derived  from  the  weathering  of  the  neigh- 
bouring rocks.  Specimens  of  very  large  size  have  been 
obtained — up  to  300  carats  ;  many  are  too  pale. 

In  the  United  States  there  are  two  areas  of  importance 
as  producers  of  Sapphires.  One  is  the  Culsagee  mine  in 
Macon  County,  North  Carolina,  where  the  mineral  occurs 
with  Spinel,  Tremolite,  Tourmaline,  Magnetite,  Kutile, 
Chromite,  Olivine,  and  Mica,  in  gneiss.  The  other  district 
is  in  Montana.  Near  Helena  is  a  glacial  moraine  known  as 
the  El  Dorado  Bar  and  in  this  Sapphire  has  been  found 
with  Topaz,  Garnet,  Cassiterite,  Quartz  and  Cyanite.  In 
addition  it  has  been  found  in  situ  in  Montana  in  a  dyke 
with  Pyrope,  at  Yogo  Creek  near  Judith  Eiver,  of  a  fine 
cornflower  blue. 

p.s.  o 


194  PEECIOUS  STONES. 

In  Australia,  New  South  Wales,  in  the  New  England  dis- 
trict, in  Diamond  localities.  Here  the  green  Corundum, 
Oriental  Emerald,  is  relatively  common — as  a  rule  it  is  one 
of  the  rarest  colours.  The  Sapphires  are  usually  of  a  very 
deep  blue.  In  Bohemia  Sapphire  has  been  found  with 
Zircon  and  Garnet. 

What  has  been  said  of  the  cutting  of  the  Euby  applies  to 
Sapphire  also.  The  fact  that  the  colour  is  of  a  richer  hue 
when  viewed  along  the  principal  axis  of  the  mineral  should 
guide  the  lapidary  in  cutting  the  stone.  Sapphires  are 
particularly  prone  to  be  patchy  in  colour,  and  bad  parts 
may  have  to  be  removed  by  slitting  before  grinding  com- 
mences. Sapphires  usually  show  a  change  of  colour  in 
artificial  light ;  some  few  specimens  change  to  violet,  thus, 
and  they  are  highly  prized.  Most  Sapphires  have  their 
colour  destroyed  by  heat,  some  very  much  more  easily  than 
others. 

The  value  of  Sapphire  of  good  quality,  and  in  carat  size, 
is  about  two-fifths  that  of  Ruby.  Moreover,  since  Sapphires 
of  large  size  are  more  plentiful  than  in  the  case  of  the  Ruby, 
there  is  not  the  same  rapid  increase  with  size.  Small 
stones  may  be  said  to  be  very  much  the  same  in  value  as 
Diamonds,  and  larger  stones  only  increase  in  about  direct 
proportion  to  their  weight. 

The  minerals  most  likely  to  be  substituted  for  Sapphires 
are  blue  lolite  (Saphir  d'Eau),  blue  Tourmaline  (Indicolite), 
and  Cyanite  (the  Sapphire  of  de  Saussure).  Less  likely  to 
be  found  under  this  name  are  blue  Topaz,  blue  Spinel, 
blue  Fluor  Spar,  blue  Quartz,  Aquamarine,  and  Haiiyne. 
Blue  Diamond  may  resemble  it  very  closely  in  colour,  but 
no  attempted  substitution  is  likely  to  be  found  in  this  case. 


PEECIOUS  STONES.  195 

With  the  exception  of  Diamond  all  are  softer  than  Corundum, 
and  Sapphire  is  the  hardest  form  of  Corundum.  Without 
exception  all  those  mentioned  are  of  lower  specific  gravity  ; 
but  Cyanite  and  Spinel  might  sink  with  Sapphire  in  a 
saturated  solution  of  iodine  and  iodoform  in  methylene 
iodide  (the  heaviest  solution  of  Max  Bauer).  Of  these  two 
Spinel  is  a  singly  refracting  mineral,  and  is  not  dichroic, 
while  Cyanite  is  less  transparent,  and  often  has  a  slightly 
pearly  lustre. 

Glass  imitations,  though  of  good  colour,  are  singly 
refracting,  and  very  much  softer  than  Sapphire. 

One  of  the  finest  and  most  perfect  Sapphires  is  the 
"Kospoli"  gem,  now  in  the  Museum  of  the  Jardin  des 
Plantes,  in  Paris;  it  weighs  132  carats.  A  stone  of  951 
carats  was  in  the  possession  of  the  King  of  Ava  at  one 
time. 

Star  Sapphire,  or  Asteriated  Sapphire.  This  is  a 
variety  which  shows  a  six-rayed  star  when  viewed  on  the 
basal  plane,  or  on  a  facet  cut  parallel  to  the  base ;  if  the 
star  is  well  defined,  and  the  rays  are  bright,  the  stone  is  of 
considerable  value ;  sometimes,  however,  it  merely  shows 
as  a  bright  band  of  light,  and  not  a  complete  star.  The 
star  characteristically  exhibits  a  shimmering  silvery  light. 
It  is  due  either  to  reflection  from  the  twin  lamellae,  which 
give  rise  to  the  parting  planes,  or  to  the  existence  of  three 
sets  of  planes  of  minute  cavities,  intersecting  one  another 
in  the  vertical  axis  of  the  crystal.  Star  Sapphires  are 
always  cut  en  cabochon. 

Leuco-Sapphire  is  colourless  crystallised  Corundum.  It 
is  in  some  cases  the  result  of  acting  on  inferior  Sapphires, 
which  are  not  of  a  colour  good  enough  for  gem  use,  by 

o  2 


196  PEECIOUS   STONES. 

heating  them  so  that  they  become  colourless.  Of  other 
gems  with  which  it  might  be  confused  Diamond  is  the  only 
one  which  will  scratch  it.  Zircon  is  the  only  one  which 
equals  it  in  density,  and  Zircon  so  far  exceeds  all  other 
gems  in  this  respect  that  it  is  easily  distinguishable. 

Oriental  Chrysolite  is  Corundum  of  the  colour  of 
Chrysolite  or  Olivine.  This  is  not  a  very  rare  tint.  It 
is  distinguished  from  ordinary  Chrysolite  by  the  greater 
hardness. 

Oriental  Emerald  is  an  emerald-green  form  of  Corundum, 
and  is  extremely  rare.  The  New  South  Wales  Sapphire 
deposits  have  produced  a  relatively  large  number.  In 
value  it  is  between  the  Sapphire  and  Kuby.  It  is  harder 
than  Emerald,  more  strongly  dichroic,  of  higher  specific 
gravity,  and  is  sometimes  fluorescent. 

Oriental  Topaz  includes  several  yellow  shades  of  Corundum, 
and  when  of  fine  reddish  yellow  colour  is  of  about  the 
same  value  as  Sapphire.  It  is  distinguished  from  Topaz 
by  higher  specific  gravity  and  greater  hardness. 

Oriental  Hyacinth  is  a  reddish  brown  variety.  It  is  also 
known  as  Vermeille  Orientale. 

Oriental  Amethyst,  also  called  the  Purple — or  Amethyst — 
Sapphire,  is  very  close  in  colour  to  the  common  Amethyst, 
but  it  shows  a  much  greater  range  of  colour  than  Amethyst 
does,  and  in  fact  may  vary  from  a  slightly  purple  red  to  a 
blue  with  a  slight  tint  of  red  in  it. 

2.  The  second  mineralogical  variety  is  Common  Corun- 
dum. It  is  less  transparent  than  the  first  variety.  The 
colour  varies  from  dull  blue  to  grey  and  from  a  rich  smoky 
brown  to  black.  It  often  has  a  very  marked  adamantine 
lustre,  and  the  brown  asteriated  form,  when  cut  en  caboehon, 


PBECIOUS  STONES.  197 

may  be  used  as  a  precious  stone.  The  coarser  varieties  are 
more  suitable  for  use  as  abrasives  than  Emery,  since  the 
latter  contains  such  softer  impurities  as  Magnetite  and 
Haematite.  It  occurs  both  in  distinct,  though  often  rough, 
crystals  and  in  large  crystalline  masses.  It  is  found  in 
many  of  the  localities  mentioned  under  Euby  and  Sapphire, 
as  Chantabun  in  Siam ;  also  on  the  Malabar  coast,  at 
Canton  in  China,  and  at  Gellivara  in  Sweden. 

8.  Emery  is  a  granular  impure  form  of  Corundum, 
containing  Magnetite  and  Haematite.  It  is  of  great 
commercial  use  as  an  abrasive,  though  now  carborundum  is 
displacing  it  in  this  use  to  a  large  extent.  It  is  found  in 
Naxos,  Samos,  and  Nicaria  in  the  Grecian  Archipelago  ;  also 
east  of  Ephesus  in  a  granular  limestone;  in  the  United 
States  at  many  places,  as  Chester  in  Massachusetts,  and  in 
Chester  County  in  Pennsylvania. 


CHAPTEK  IX. 

234.    SPINEL    AND    CHRYSOBERYL. 

SPINEL  included  some  of  the  gems  called  Lychnis  by 
Pliny,  and  his  Carbunculi  Amethystizontes  were  Spinels 
also.  Though  it  has  been  known  as  a  gem  stone  since 
remote  times,  it  was  till  the  eighteenth  century  confused 
with  other  species. 

As  met  with  in  jewellery,  the  characteristic  colour  is 
flame-red ;  this  form  is  sometimes  distinguished  as  Spinel 
Kuby  or  Euby  Spinel;  lighter  rose-red  shades  are  called 
Balas  Kuby ;  specimens  of  a  violet  tint  are  known  as 
Almandine  Spinels  or  sometimes  Alabandin  Kuby  (from 
Alabandin  in  Caria) ;  blue  stones  are  known  as  Spinel 
Sapphire,  and  the  orange-red  ones  as  Kubicelle ;  a  colour- 
less variety  is  sometimes  seen.  Other  colours  occur  in 
the  mineralogical  varieties,  Pleonaste,  Chlorospinel  and 
Picotite. 

The  lustre  of  the  gem  varieties  is  vitreous,  and  often 
splendent,  and  they  are  transparent  or  subtransparent  ; 
the  other  varieties  may  occur  almost,  if  not  quite,  opaque. 

It  is  singly  refracting,  hence  shows  no  dichroism,  and 
under  the  polariscope  the  field  remains  dark  when  the 
specimen  is  rotated  under  crossed  Nicol's  prisms.  It 
phosphoresces  with  a  red  light.  Its  index  of  refraction  for 
yellow  light  is  1*72,  and  the  dispersion  is  small. 

Qn    rubbing    it   shows    a    surface   charge    of    positive 


PRECIOUS  STONES.  199 

electricity,  but  not  to  any  great  degree.     It  is  not  fusible 
before  the  ordinary  blow-pipe. 

The  specific  gravity  is  3'60  to  -3'63,  rather  higher  than 
the  Diamond.  The  fracture  is  conchoidal,  and  there  is  a 
very  imperfect  octahedral  cleavage.  It  is  a  brittle  mineral, 
though  its  hardness  is  considerable,  being  equal  to  8  of 
Mohs'  scale.  The  streak  is  white. 

The  crystalline  form  is  cubic,  and  the  usual  habit  octa- 
hedral (Fig.  15) ;  very  rarely  is  the  habit  cubic;  the  faces 
of  the  octahedron  are  sometimes  curved ;  twinning  of  the 
crystals  is  commonly  seen.  Crystals  are 
usually  idiomorphic  and  completely 
developed.  An  intimate  lamellar  struc- 
ture is  sometimes  seen,  due  to  repeated 
twinning  in  one  plane. 

In    origin    it    is   very   closely   allied 
with   Corundum,   being    usually   found 

in    limestones   altered    by    thermo-    or 

J  FIG.  15.— Spinel, 

dynamo-metamorphism,  thus  naturally 

its  associates  are  the  same  as  Corundum  usually  has. 

In  chemical  composition  it  is  a  combination  of  the  oxides 
of  magnesium  and  aluminium,  MgO,  A1203.  The  colour  is 
due  in  all  cases  to  the  presence  of  other  substances ;  thus 
traces  of  chromium  or  iron  may  cause  a  red  colour ;  these 
metals  are  not  so  much  impurities  as  replacement  products, 
for  some  of  the  aluminium  may  be  replaced  by  ferric  iron 
or  chromium,  and  some  of  the  magnesium,  by  the  iron  (in 
a  ferrous  condition)  or  by  manganese.  We  thus  get  three 
other  mineralogical  varieties.  Euby  Spinel  or  Magnesium 
Spinel  being  the  first,  the  second  is  an  Iron-Magnesium 
Spinel,  and  is  known  as  Ceylonite  or  Pleonaste  ;  it  is  usually 


200  PKECIOUS  STONES. 

of  dark  colour,  varying  from  green  to  very  deep  brown  or 
even  black.  The  third  variety  is  one  in  which  iron  replaces 
aluminium ;  it  is  called  Chlorospinel  from  its  green  colour, 
this  colour  being  due  to  the  presence  of  traces  of  copper. 
The  fourth  variety,  Picotite,  has  replacements  by  both  iron 
and  chromium  ;  its  chemical  formula  may  be  expressed 
(MgFe)O,  (AlCr)203. 

When  heated  the  red  varieties  become  brown  ;  on  cooling 
again  the  red  colour  is  restored,  the  mineral  passing 
through  green  and  colourless  stages. 

The  distribution  of  Spinel  is  very  similar  to  that  of  Ruby 
and  Sapphire.  Thus  it  is  found  in  Burma,  in  the  gem 
gravels  of  Ceylon,  and  in  New  South  Wales.  Other  localities 
are  Balachan  (or  Badakshan)  in  Usbec  Tartary,  Pegu, 
Mysore,  and  Minas  Novas  in  Brazil.  In  Sweden  it  is  found 
at  Aker  in  Sodermanland  in  blue  crystals  (Akerite). 

Spinel  is  cut  either  as  a  brilliant  or  in  the  step  pattern ; 
when  cut  it  may  be  mistaken  for  several  other  minerals ; 
thus  the  Buby  Spinel  and  some  of  the  Garnets  are  very 
similar,  both  being  singly  refracting,  but  Garnet  has  a 
higher  specific  gravity,  and  it  is  also  less  hard  than  Spinel. 
From  red  Topaz  the  Balas  Ruby  may  be  distinguished  by 
the  Topaz  being  doubly  refracting  and  dichroic,  and  also 
more  strongly  charged  with  electricity  when  rubbed.  The 
word  "  Balas  "  is  said  to  be  derived  from  the  place  name 
Balachan.  Spinel  and  Corundum  of  a  violet  colour  can  be 
distinguished  by  the  single  refraction  of  the  former  and 
the  dichroism  of  the  latter. 

Spinels  take  a  high  polish  when  cut,  and  when  large 
their  value  is  considerable.  The  Ruby  Spinel  when  above 
three  carats  approaches  the  Ruby  in  value,  but  below  that 


PEECIOUS   STONES.  201 

weight  it  is  only  worth  about  half  as  much  as  a  good  Kuby. 
Balas  Euby  is  worth  about  a  quarter  of  the  true  Euby  of 
the  same  weight.  What  was  probably  the  largest  known 
Spinel  of  fine  quality  was  one  exhibited  at  the  1862  Exhibi- 
tion in  London;  it  was  cut  en  cabochon  and  weighed  197 
carats.  Another  large  one  is  said  to  have  been  in  the 
Treasury  of  St.  Denis,  and  the  shield  of  the  Shah  of  Persia 
had  a  very  brilliant  Spinel  at  its  lower  point.  A  famous 
engraved  specimen  was  one  in  the  Khodes  Gems  carved  with 
a  Gorgon's  head. 

242.  CHRYSOBEEYL. 

This  stone  was  not  the  Chrysoberyl  of  the  ancients,  which 
was  probably  either  our  Chrysoprase  or  our  Chrysolite. 

Chrysoberyl  is  a  mineral  of  greenish  colour,  variously 
seen  as  grass-green,  asparagus-green,  greenish-white,  yellow- 
green,  or  even  emerald-green — rarely  colourless  ;  the  darker 
rich  green  kinds  are  known  as  Alexandrite,  they  have  a 
columbine-red  colour  by  transmitted  light.  Another  variety 
is  the  Cymophane  or  true  Cat's  Eye,  which  shows  a  beautiful 
blue  chatoyancy.  Chrysoberyl  is  rather  rare  in  good  speci- 
mens and  is  highly  prized;  were  it  more  known  its  popularity 
would  most  likely  be  greater  still.  Where  the  surfaces  are 
bright  it  is  often  seen  to  be  transparent,  but  since  as  a  rule 
it  is  only  found  in  water-worn  fragments  and  rolled  crystals 
its  more  common  appearance  may  be  likened  to  a  piece  of 
glass  that  has  been  similarly  water-worn ;  some  specimens 
are  but  sub-translucent. 

It  has  two  optic  axes  or  directions  in  which  light  can 
travel  with  equal  velocities,  and  its  greatest  index  of  refrac- 
tion is  1-756  and  its  least  T747 ;  its  dispersive  power  is 


202  .PEECIOUS  STONES. 

small.  Ordinary  Chrysoberyl  is  but  feebly  dichroic,  but 
Alexandrite  shows  marked  dichroism  even  to  the  unaided 
eye ;  when  viewed  in  artificial  light  in  the  direction  of  the 
shortest  crystallographic  axis  the  colour  is  columbine-red, 
though  in  daylight  the  general  tint  is  green  ;  and  in  this 
direction,  too,  the  dichroscope  gives  two  distinctly  coloured 
images,  one  emerald  green  and  the  other  yellow,  while  in 
another  direction  a  columbine  red  colour  is  seen.  The 
Alexandrite  is  not  only  dichroic,  but  trichroic. 

Alone  it  is  infusible  before  the  blowpipe  and  its  colour 
remains  unchanged  when  heated.  When  rubbed  it  shows 
a  charge  of  positive  electricity,  which  is  retained  for  longer 
than  is  usually  the  case  with  minerals. 

The  specific  gravity  is  3*68  to  3'75 ;  the  fracture  is 
conchoidal  to  uneven ;  it  has  a  distinct  cleavage  parallel 
to  one  and  cutting  the  other  two  crystal  axes ;  it  is  brittle  but 
very  hard,  ranking  in  point  of  hardness  between  the  Topaz 
and  Sapphire,  or  equal  to  8J.  The  streak  is  colourless. 

In  crystalline  form  it  is  rhombic  and  when  in  single 
crystals  its  habit  is  tabular,  the  faces  normal  to  the  shortest 
axis  being  largely  developed  and  showing  striations  parallel 
to  the  vertical  axis.  More  often  the  crystals  are  twinned, 
either  in  three-lings  or  six-lings,  so  as  to  give  a  pseudo- 
hexagonal  appearance  to  the  group. 

The  variety  Cymophane  shows  an  interesting  minute 
structure ;  this  consists  of  a  multitude  of  very  small  pores 
or  cavities  in  the  crystal  arranged  in  a  definite  way,  giving 
a  certain  degree  of  cloudiness  to  these  specimens  and  also 
causing  the  opalescent  effect  seen  on  moving  the  stone. 
When  the  band  of  light  is  very  sharply  defined  the  stone 
showing  it  is  called  a  Cat's  Eye. 


PEECIOUS  STONES.  203 

Chrysoberyl  has  rarely,  if  ever,  been  found  in  situ,  but 
the  secondary  deposits  in  which  it  occurs  are  so  constantly 
those  derived  from  the  weathering  of  granite  and  gneissose 
rocks  that  there  is  little  doubt  it  is  in  such  rocks  that  it  has 
its  origin.  The  principal  locality  for  Chrysoberyl  of  the 
ordinary  variety  is  the  state  of  Minas  Geraes  in  Brazil, 
where  it  is  met  with  sometimes  in  association  with  Diamond. 
More  often  the  associates  are,  Quartz  and  its  varieties, 
Tourmaline,  Euclase,  Topaz,  Garnet,  and  Spinel.  In  Con- 
necticut, at  Haddam,  it  occurs  with  Tourmaline,  Garnet, 
and  Beryl,  in  granitic  bands  in  gneiss.  In  Moravia  it  is 
found  at  Marschendorf.  An  important  locality  is  in  the 
Ural  Mountains,  about  sixty  miles  east  of  Ekaterinburg, 
associated  with  Topaz  and  Euclase.  Here  the  variety 
Alexandrite  is  found,  with  Emerald,  in  mica-schist  close  to 
granite.  Alexandrite  was  named  after  Alexander  II.  of 
Eussia.  More  recently  it  has  been  found  in  the  southern 
Urals.  Much  of  the  Chrysoberyl  that  is  suitable  for  gem 
use  is  found  in  Ceylon  in  the  gem  gravels  in  rolled  pieces. 
Here  all  three  forms  are  found,  the  ordinary  variety  of 
different  tints  of  green,  the  chatoyant  variety  Cymophane, 
and  Alexandrite.  The  Cymophane  is  known  sometimes  as 
Ceylon  Cat's  Eye  or  Oriental  Cat's  Eye,  to  distinguish  it 
from  the  Quartz  Cat's  Eye. 

In  chemical  composition  Chrysoberyl  is  beryllium 
aluminate  BeO,  A1203.  The  ordinary  variety  contains 
iron  usually,  and  the  variety  Alexandrite  is  supposed 
to  owe  its  colour  to  traces  of  chromium  oxide. 

Chrysoberyl  is  one  of  the  minerals  used  as  pivot  bearings 
in  watches  and  chronometers.  Its  use  in  jewellery  is  much 
subject  to  the  fashion  of  the  moment,  and  the  demand 


204  PKECIOUS   STONES. 

varies  considerably  in  different  countries  ;  thus  in  Brazil  it 
is  esteemed  the  most  valuable  of  the  coloured  gems.  In 
Eussia  again  the  Alexandrite  is  in  great  demand.  Chryso- 
beryl is,  perhaps,  the  only  coloured  stone  which  shows  to 
the  best  advantage  when  cut  as  a  brilliant ;  when  the  gem 
is  thick  enough  this  form  is  adopted,  but  thin  specimens 
may  be  cut  in  gentle  steps,  or  a  mixed  cut  may  be  used  ;  it 
is  usually  mounted  in  a  closed  setting.  Cymophane  and 
Cat's  Eye  are  cut  en  cabochon  with  a  well-marked  curvature. 
In  cutting  the  Alexandrite  due  thought  must  be  given  to 
the  colours  as  they  will  appear  in  different  directions.  The 
finest  Cat's  Eye  known  was  in  the  collection  of  Mr.  H.  P. 
Hope,  to  which  collection  the  famous  Blue  Hope  Diamond 
belonged.  Alexandrites  have  been  found  up  to  60  carats. 

Chrysoberyl  can  be  distinguished  from  Chrysolite  (or 
Peridot)  by  the  greater  hardness  and  rather  higher  specific 
gravity  of  the  Chrysoberyl.  The  chatoyant  variety  is  dis- 
tinguished from  the  Cat's  Eye  variety  of  Quartz  most  easily 
by  the  much  lower  specific  gravity  of  the  Quartz. 


CHAPTER  X. 

270.    CALCITE. LABRADOKITE. 

THIS  mineral,  so  important  in  general  mineralogy,  is 
of  but  small  consequence  in  so  far  as  its  use  as  a  precious 
stone  goes.  A  great  deal  of  the  material  known  to 
Theophrastus,  Pliny,  and  other  ancient  writers,  belonged 
to  this  species.  A  complete  mineralogical  description  is 
here  uncalled  for,  as  the  crystallised  varieties  are  practically 
beyond  the  range  of  our  subject,  only  some  of  the  many 
massive  varieties  being  used. 

When  pure  it  is  colourless,  but,  like  so  many  other 
colourless  minerals,  it  is  subject  to  much  variation  in 
colour  from  impurities,  even  when  these  are  in  very  small 
quantity.  Thus  it  may  be  cream,  pink,  grey,  green,  blue, 
violet,  yellow,  brown,  etc.  The  lustre  of  pure  specimens  is 
vitreous ;  impure  forms  may  be  earthy.  Similarly  all 
gradations  from  transparent  to  opaque  are  seen. 

One  of  its  outstanding  physical  properties  is  its  remark- 
ably pronounced  double  refraction,  and  this  property  has 
given  the  name  Doubly  Refracting  Spar  to  one  of  the 
varieties.  The  refractive  indices  for  the  D  line  of  the 
spectrum  are,  for  the  ordinary  ray  1*658,  and  for  the  extra- 
ordinary ray  1*486.  On  heating  it  decrepitates,  and  turns 
opaque  white  ;  coloured  varieties  may  change  colour.  The 
specific  gravity  is  2*71  to  2*72  in  pure  varieties,  but  may 
be  up  to  2*84  in  impure  forms.  The  hardness  is  3.  It 


206  PKECIOUS   STONES. 

shows  a  conchoidal  fracture  when  a  fracture  at  all  is  obtained, 
but  owing  to  a  highly  perfect  cleavage  a  true  fracture  is 
not  often  seen.  This  cleavage  is  parallel  to  the  faces  of  the 
rhombohedron,  and  advantage  is  taken  of  it  in  preparing 
Calcite  prisms  for  the  dichroscope  and  the  polariscope. 
The  streak  is  white.  The  crystalline  form  is  rhombohedral, 
and  the  mineral  often  occurs  in  a  great  variety  of  highly 
developed  crystals.  The  crystals  are  normally  attached, 
and  hence  not  fully  developed. 

Its  modes  of  origin  are  very  various,  but  the  two 
chief  ones  are  those  due  first  to  the  uprising  of  heated 
water,  and  secondly,  to  the  downward  percolation  of  water 
usually  at  moderate  temperature.  In  its  hypogene  form  it 
is  associated  with  many  metalliferous  ores,  and  in  its 
epigene  form  with  the  great  array  of  minerals  formed  by 
decomposition  and  subsequent  new  chemical  combination. 

The  chemical  composition  is  calcium  carbonate,  CaC03. 
Some  of  the  calcium  is  frequently  replaced  by  iron, 
magnesium,  lead,  manganese,  or  zinc. 

The  normal  crystallised  variety  only  concerns  us  in  so 
far  as  it  is  used  for  the  optical  instruments  before  mentioned. 
For  this  purpose  the  large  cleavage  rhombs  from  the 
Icelandic  localities  on  the  Eskefjord  and  Breitifjord  are 
used,  but  the  material  is  now  becoming  scarce. 

The  fibrous  variety  known  as  Satin  Spar  is  of  more 
special  interest ;  the  fibres  are  very  fine,  and  are  arranged 
in  a  parallel  manner  so  as  to  exhibit  a  silky  effect  when 
the  specimen  is  broken ;  some  forms  show  a  wavy  band  of 
light  also,  and  the  appearance  may  then  be  compared  to 
"watered"  silk.  The  cause  of  this  phenomenon  is  the 
same  as  in  other  chatoyant  minerals,  namely,  reflection 


PEECIOUS  STONES.  207 

from  a  vast  number  of  minute  parallel  surfaces.  Amongst 
other  localities  are  the  Carboniferous  volcanic  rocks  of 
Fifeshire,  and  in  veins  in  the  "plate"  or  lower  Carboniferous 
shales  of  Alston  Moor,  in  Cumberland.  It  is  nearly  always 
found  in  narrow  veins,  and  usually  completely  fills  them. 
It  may  be  cut  en  cabochon,  to  show  the  chatoyant  effect,  but 
its  softness  renders  it  very  prone  to  damage. 

Of  the  massive  varieties  Fire-marble,  or  Lumachello,  may 
be  noticed.  It  is  a  fossiliferous  marble,  with  a  beautiful 
iridescence  of  red,  green,  and  blue  colours,  almost  com- 
parable to  the  Opal.  It  is  chiefly  found  in  the  lead  mines 
of  Bleiberg,  in  Carinthia. 

What  was  known  to  Pliny  as  the  Alabastrites  was  a  form 
of  carbonate  of  calcium,  deposited  from  water,  in  layers. 
It  might  be  either  stalactitic  (formed  by  lime-bearing  water 
dripping  from  the  roof  of  a  cave),  or  stalagmitic  (formed 
by  the  water  dripping  on  the  floor).  When  it  showed  pale 
creamy  bands  it  was  known  as  Onyx,  from  its  resembling 
the  finger-nails  of  the  "well-bred  person."  The  term 
Alabaster  was  used  on  account  of  this  substance  frequently 
forming  the  material  of  the  Alabastra  or  ointment  jars 
(King).  Much  of  this  Alabaster  was  found  near  Thebes, 
and  has  thus  come  to  be  known  as  Egyptian  Alabaster,  to 
distinguish  it  from  the  compact  Gypsum,  which  is  also 
called  Alabaster.  Much  of  this  stalactitic  material,  when 
first  formed,  is  probably  Aragonite,  a  rhombic  carbonate  of 
calcium  which  tends  to  pass  into  Calcite.  Alabaster  is 
translucent,  and  is  capable  of  taking  a  very  fine  polish,  but 
on  account  of  its  softness  it  is  easily  scratched.  "Gibraltar 
Stone"  and  "Mexican  Onyx"  are  named  from  the  localities 
where  they  are  found. 


208  PEECIOUS  STONES. 

Travertine  is  a  form  deposited  by  springs  and  streams. 
The  name  is  derived  from  Lapis  Tiburtinus  of  Pliny,  much 
of  the  material  being  found  near  Tivoli.  It  shows  the 
same  banded  structure. 

288.  MALACHITE. 

The  Malachites  of  Pliny  were  not  our  Malachite,  but  his 
Smaragdus  Medicus  has  been  identified  by  King  as  the 
mineral  now  under  consideration,  and  the  Chrysocolla  of 
Theophrastus  seems  to  have  been  Malachite  in  part.  In 
the  time  of  De  Boot  it  was  held  in  great  esteem  for  variou 
medicinal  properties  attributed  to  it — virtues  which  had 
previously  been  held  to  belong  to  a  variety  of  Jasper,  but 
which  were  by  the  magicians  transferred  to  Malachite, 
when  that  particular  Jasper  could  not  be  obtained.  It  is  of 
a  rich  bright  green  in  colour,  some  varieties  being  banded 
with  lighter  and  darker  greens.  The  massive  botyroidal 
variety,  chiefly  used  as  an  ornamental  stone,  has  a  lustre 
that  may  be  silky  when  the  fibrous  structure  is  marked,  or 
waxy  when  very  compact.  The  crystals,  which  are  usually 
very  minute,  are  adamantine  or  vitreous  in  lustre.  It  is 
translucent  to  opaque ;  when  heated  it  turns  black  and 
readily  fuses.  The  specific  gravity  is  high,  3*71  to  4*01. 
The  crystalline  form  is  mono-symmetric,  the  crystals  are 
minute  and  acicular. 

It  occurs  as  a  decomposition  product  of  copper  ores,  and 
is  often  found  in  pseudomorphs  of  the  minerals  Cuprite  and 
Azurite.  It  is  associated  with  the  closely  related  mineral 
Azurite  in  most  cases ;  although  it  may  be  found  in  any 
copper-bearing  vein,  whose  contents  have  undergone 
alteration,  and  as  an  alteration  product  of  the  disseminated 


PRECIOUS   STONES.  209 

copper  in  some  sedimentary  rocks,  and  is  thus  widely 
distributed ;  yet  specimens  suitable  for  ornamental  use  are 
not  at  all  common,  most  of  them  being  found  in  the  Ural 
Mountains  ;  thus  at  Nizhni  Tagilsk,  one  mass  was  found 
measuring  some  160  square  feet,  on  the  upper  surface. 
Now  but  few  of  the  mines  produce  it  in  pieces  large  enough 
to  cut.  On  the  west  coast  of  Africa,  Bembe  has  yielded  fine 
pieces.  In  Australia,  the  Cobar  mines  in  New  South  Wales 
and  the  Burra-Burra  mines  in  South  Australia  produce  good 
specimens.  In  the  United  States,  the  Humming  Bird  mine 
in  Arizona  is  a  noted  locality. 

In  composition  it  is  a  basic  cupric  carbonate,  CuCo3, 
Gu(OH)2,  containing  72  per  cent,  of  oxide  of  copper.  The 
darkening  seen  on  heating  is  due  to  the  driving  off  of  water. 
It  is  easily  reduced  to  metallic  copper,  hence  is  a  valuable 
ore  of  that  metal  when  occurring  in  sufficient  quantity. 

A  few  intagli  in  Malachite  are  known;  now  its  chief 
ornamental  use  is  for  such  articles  as  vases,  letter  weights 
and  other  smaller  objects  ;  often  it  is  used  as  a  veneer  and 
for  inlaying ;  rarely  is  it  cut  as  a  gem  stone ;  when  it  is,  it 
is  usually  en  cabochon,  more  rarely  in  steps. 

THE  FELSPABS. 

The  Felspar  Group  contains  several  closely  related  species 
which  are  of  secondary  importance  as  precious  stones.  The 
individual  members  closely  resemble  one  another  in 
crystalline  form,  cleavage,  hardness  and  specific  gravity, 
and  to  some  extent  in  origin,  though  some  are  characteristic 
of  one  type  of  rock,  and  some  of  another.  All  we  are 
concerned  with  belong  to  the  triclinic  system,  with  one 
exception,  that  being  Qrthoclase,  In  all,  the  common 

P.S,  P 


210  PEECIOUS  STONES. 

habit  of  the  crystal  is  that  of  a  stout  prism  terminated  by 
one  or  more  faces  in  an  oblique  direction,  the  exact  angles 
varying  but  little  in  the  different  members  of  the  group. 
All  possess  two  cleavages  ;  in  Orthoclase  these  cleavages  are 
at  right  angles  to  one  another,  while  in  the  other  Felspars 
the  angle  does  not  differ  widely  from  a  right  angle.  The 
hardness  of  all  is  equal  to,  or  slightly  exceeds,  6  of  Mohs' 
scale.  The  specific  gravity  varies  between  2'5  and  2'9.  All 
are  silicates  of  aluminium  with  either  potassium,  sodium 
or  calcium.  Further,  there  is  a  certain  amount  of  gradation 
seen  from  one  member  of  the  group  to  another,  and  this  is 
accompanied  by  a  corresponding  gradual  change  in  form 
and  physical  properties.  Few  of  the  Felspars  show  trans- 
parency, most  are  translucent  to  opaque ;  most  are  of  a  light 
colour  or  colourless.  Several  different  members  of  the 
group  are  used  as  precious  stones  under  the  same 
designation. 

313.  ORTHOCLASE. 

Orthoclase  occurs  in  several  shades  of  colour,  usually 
light  in  tint ;  rarely  it  is  colourless,  as  in  the  pure  variety 
Adularia,  which  also  shows  a  moderate  degree  of  trans- 
parency, other  kinds  being  translucent  to  opaque.  Doubly 
refracting ;  specific  gravity  2'53  to  2'59;  two  cleavage  planes 
at  right  angles  to  one  another,  both  well  marked.  Streak 
colourless.  Its  crystalline  form  belongs  to  the  monosym- 
metric  system ;  the  crystals  are  sometimes  attached,  often 
crystallised  from  a  semi-fluid  magma  and  then  frequently 
completely  developed.  It  is  an  essential  rock-forming  con- 
stituent of  several  volcanic  rocks.  In  chemical  composition 
it  is  an  aluminium  potassium  silicate,  K20,  A1203,  6  Si02. 


PKECIOUS  STONES. 


211 


The  most  important  variety  for  the  present  purpose  is  the 
pure  Adularia,  which  is  often  found  in  large  transparent  or 
sub-transparent  crystals  attached  to  the  matrix  in  groups, 
the  crystals  often  being  twinned  (Fig.  16).  It  is  of  frequent 
occurrence  in  the  fissures  of  the  gneissose  rocks  of  the  Alps. 
The  sub-variety  Moonstone  shows  a  peculiar  reflection  of 
bluish-white  light,  which  from  its  common  presence  in 


FIG.  16. — Adularia. 

Adularia  is  known  as  adularescence ;  it  is  only  seen  in 
certain  directions  and  chiefly  near  the  face  which  is  normal 
to  the  shorter  lateral  axis  of  the  crystal.  Moonstone, 
which  is  also  known  as  Girasol,  Wolf's  Eye,  Ceylonese 
Opal,  and  Water  Opal,  is  not  only  a  variety  of  Adularia ; 
the  term  refers  to  the  appearance  of  the  stone  rather  than 
to  its  composition,  and  other  Felspars,  as  Albite  and 

p  2 


212  PRECIOUS  STONES. 

Oligoclase,  may  occur  as  Moonstone.  The  most  important 
locality  for  this  gem  variety  is  to  the  south-east  of  Adam's 
Peak  in  Ceylon,  where  Moonstone  occurs  in  fragments 
imbedded  in  a  white  clay,  probably  derived  from  the 
weathering  of  some  acid  volcanic  rock.  Another  place 
where  it  is  found  is  the  Amelia  Court  House  in 
Virginia  in  the  United  States;  here  it  occurs  in  situ  in 
the  granite. 

It  is  always  cut  either  in  flat  pieces,  when  it  shows  a 
uniform  adularescence,  or  en  cabochon,  when  the  light  takes 
the  form  of  a  more  or  less  well  marked  band.  The  exposed 
surface  must  be  properly  placed  to  show  the  full  effect. 
Brand  records  that  a  good  Moonstone  of  about  half  an  inch 
in  diameter  sold  for  £35.  It  is  readily  distinguished  from 
a  glass  imitation  by  the  double  refraction  of  the  Felspar, 
and  by  the  glass  being  more  dense. 

Earely  Orthoclase  occurs  in  the  form  of  Aventurine,  very 
similar  in  appearance  to  the  Aventurine  variety  of  Quartz. 
The  effect  is  due  to  the  inclusion  along  the  directions  of  the 
more  perfect  cleavage  plane  of  numerous  plates  of  micaceous 
Haematite  which  cause  a  bright  red  metallic  reflection  of 
the  light.  Aventurine  Felspar  is  also  known  as  Sunstone, 
and  here  again  the  term  applies  to  appearance  rather  than 
to  composition.  Orthoclase  Sunstone  is  not  so  common  as 
the  Oligoclase  Sunstone.  The  Orthoclase  variety  is  found 
chiefly  in  North  America,  at  Amelia  Court  House  in 
Virginia  and  in  New  York  State.  It  is  cut  en  cabochon,  and 
the  surface  must  of  course  be  in  such  a  position  that  the 
reflection  is  seen  at  its  best. 

A  rare  variety  of  Orthoclase  is  that  which  shows  an 
optical  colour  effect  similar  to  that  seen  in  Labradorite,  and 


PEECIOUS  STONES.  213 

hence  known  as  labradorescence.  It  is  found  in  augite- 
syenite  at  Laurvik  in  Norway,  and  though  not  much  used 
for  cutting  in  small  pieces,  it  is  frequently  to  be  seen  in 
this  syenite,  slabs  of  which  are  largely  used  now  in  facing 
the  jambs  and  lintels  of  shops  in  large  towns. 

All  these  varieties  of  Orthoclase  may  be  distinguished  from 
similar  varieties  of  triclinic  Felspars  by  the  absence  of  the 
characteristic  striping  of  these  latter  species. 

315.  MICROCLINE. 

This  Felspar  occurs  white,  cream  coloured,  red,  and  green : 
the  only  kind  with  which  we  are  concerned  is  the  green, 
which  is  known  as  Amazonstone.  The  exact  colour  varies 
somewhat,  but  may  usually  be  described  as  a  verdigris 
green  ;  it  is  sub-translucent  to  opaque.  The  specific  gravity 
is  2*54  to  2*57.  It  has  a  vitreous  lustre,  uneven  fracture, 
and  the  hardness  is  6  to  6j.  Besides  the  cleavages  all 
Felspars  show  it  has  two  other  less  perfect  cleavages.  It 
often  shows  a  characteristic  corded  structure,  and  it  crystal- 
lises in  triclinic  forms.  Its  mode  of  occurrence  and 
composition  are  very  similar  to  Orthoclase,  but  the  colour 
is  supposed  to  be  due  to  traces  of  copper  compounds.  In 
the  Ural  Mountains  it  is  found  near  Minsk ;  in  North 
America,  at  Pike's  Peak  in  Colorado,  and  with  other  Fel- 
spars at  Amelia  Court  House  in  Virginia.  Fine  crystals 
were  obtained  by  Professor  Heddle  near  Tongue  in 
Scotland.  It  is  cut  for  small  ornamental  objects  and  for 
brooches,  rings,  and  the  like.  In  the  latter  cases  the 
usual  form  given  is  that  of  a  thin  plate  either  flat  or 
curved. 


214  PEECIOUS  STONES. 

316.  ALBITE. 

Albite  is  usually  colourless  or  white  when  unweathered, 
but  may  show  tints  of  pink,  grey,  red,  or  green.  It  is 
transparent  to  sub-translucent.  The  specific  gravity  is  2'62 
to  2*65,  with  a  fracture  and  cleavages  very  similar  to  those 
of  other  members  of  the  group.  The  hardness  is  6  to  6J. 
It  is  a  triclinic  Felspar  and  is  usually  twinned  repeatedly 
in  fine  lamella,  and  this  gives  rise  to  a  striped  appearance 
often  seen  in  the  triclinic  Felspars.  As  an  original  con- 
stituent of  many  granites  it  is  very  widely  distributed  ;  in 
these  cases  it  is  usually  in  crystalline  masses  that  have 
been  formed  simultaneously  with  other  minerals,  and  as  a 
consequence  the  crystal  faces  are  not  developed.  Again,  it 
may  frequently  be  found  in  cavities  in  the  granites,  usually 
in  the  outer  part  of  the  mass,  associated  with  Beryl,  Topaz, 
Smoky  Quartz  and  other  minerals.  In  chemical  composi- 
tion it  is  an  aluminium  sodium  silicate,  Na20,  A1203,  6  Si02. 
An  Aventurine  variety  sometimes  occurs,  but  more  impor- 
tant is  the  purer  form  Peristerite  or  Albite  Moonstone, 
which  shows  the  chatoyant  light  very  well  in  good  specimens. 
Other  specimens  show  more  play  of  colour  like  Labradorite, 
but  less  intense.  Peristerite  occurs  at  Bathurst  and 
Burleigh  in  Ontario  and  at  several  other  places  in  North 
America. 

317.  OLIGOCLASE. 

This  species  is  chiefly  of  interest  because  to  it  belong 
most  of  the  Sunstones  met  with  in  use  as  precious  stones. 
Its  composition  varies  somewhat ;  it  is  essentially  an 
aluminium-sodium-calcium  silicate.  It  is  usually  white, 
grey,  greenish,  or  reddish  in  colour,  transparent  to  sub- 


PRECIOUS   STONES.  215 

translucent,  of  specific  gravity  2'63  to  2'67.  Its  hardness 
is  rather  greater  than  the  previous  species,  being  6 — 7. 
The  cleavages  are  very  similar  to  those  of  other  triclinic 
Felspars.  It  occurs  in  well  developed  crystals  of  the 
triclinic  system,  and  in  crystalline  masses.  In  the 
Aventurine  variety  (Heliolite)  the  inclusion  is  usually 
Haematite,  possibly  sometimes  Gothite,  but  it  always  occurs 
so  as  to  give  the  sheen  parallel  to  the  principal  cleavage 
plane;  on  this  aspect,  too,  it  shows  the  characteristic 
striping  due  to  poly  synthetic  twinning  common  to  all 
triclinic  Felspars.  This  striping  affords  a  means  of  dis- 
tinguishing Oligoclase  Sunstone  from  the  artificial  glass 
and  from  the  Aventurine  Quartz ;  from  the  glass  it  may 
also  be  distinguished  by  its  double  refraction.  Quartz  is 
usually  distinctly  harder  also  than  Oligoclase.  It  was  at 
first  only  known  from  Cedlovatoi,  an  island  near  Arch- 
angel. At  that  time — early  in  the  nineteenth  century — it 
was  in  great  demand,  and  brought  a  high  price.  Later  it 
was  found  near  Lake  Baikal,  and  at  Tvedestrand  in  Norway. 
It  also  occurs  in  County  Donegal,  and  in  the  island  of  Tiree 
in  Scotland.  There  are  several  localities  where  it  is  found 
in  North  America.  It  is  cut  en  caboclion,  so  as  to  expose 
the  metallic  reflection  to  the  observer. 

319.  LABEADORITE. 

This  Felspar  is  rarely  seen  in  distinct  crystals,  more  often 
in  large  crystalline  masses  of  a  dull  grey  or  brownish  colour, 
very  rarely  colourless ;  the  general  lustre  is  vitreous ;  very 
rarely  is  it  seen  transparent,  usually  being  only  sub-trans- 
lucent, or  even  opaque.  It  has  two  cleavages  inclined  to 
one  another  at  a  little  over  a  right  angle,  and,  in  addition, 


216  PRECIOtJS  STONES. 

there  are  three  other  less  important  cleavage  planes ;  the 
lustre  of  the  more  perfect  cleavage  plane  is  distinctly 
pearly.  From  the  less  perfect  cleavage,  on  turning  in 
certain  directions  most  beautiful  colours  will  be  suddenly 
seen  proceeding  when  the  angle  the  line  of  sight  makes 
with  the  cleavage  plane  is  exactly  right ;  in  all  other 
positions  the  mineral  is  but  a  dull  grey  colour.  This  effect, 
from  being  seen  in  this  mineral,  is  known  as  labradores- 
cence  ;  the  colours  are  very  varied — green,  yellow,  blue,  or 
red,  and  these  in  various  shades  may  be  seen.  The  colour 
in  some  cases  is  due  to  minute  inclusions  causing  interfer- 
ence of  light ;  but  in  the  case  of  the  blue  colour  it  must  be 
due  to  some  other  cause  of  interference,  since  it  may  be 
seen  when  there  are  no  inclusions  present. 

The  specific  gravity  of  Labradorite  is  2*67  to  2'76 ;  its 
hardness  is  rather  below  the  average  of  the  Felspars,  being 
only  5  to  6.  In  crystalline  form  it  is  triclinic,  and  it  often 
shows  repeated  twinning,  and  this  may  cause  the  flash  of 
light  to  be  broken  up  by  rectangular  patches  of  dull  grey, 
representing  a  portion  of  the  crystal  occupying  a  reversed 
position ;  when  the  specimen  is  turned  the  parts  which 
were  previously  grey  may  be  seen  to  light  up  with  colour 
and  at  the  same  time  the  previously  brilliant  portions  will 
be  dull. 

In  chemical  composition  it  is  an  aluminium-calcium- 
sodium  silicate ;  it  is  a  common  constituent  of  basic  erup- 
tive rocks.  It  was  first  found  in  the  island  of  St.  Paul,  off 
the  east  coast  of  Labrador ;  on  the  mainland  of  Labrador 
several  localities  near  Nain  are  given.  In  Eussia  it  was 
found  in  boulders  at  Peterhof,  and  in  some  of  the  cobbles 
used  in  paving  the  St.  Petersburg  streets.  Other  localities 


PEECIOtTS  STONES.  217 

are  Miolo  and  Abo,  in  Finland ;  in  the  gabbro  of  the  Kiver 
Teterev,  a  tributary  of  the  Dnieper ;  and  in  many  places  in 
the  United  States. 

The  material  from  the  United  States  is  largely  quarried 
as  an  ornamental  stone,  but  is  inferior  in  brilliance  of 
colour  to  the  Labrador  specimens,  and  hence  is  not  cut  as  a 
gem ;  for  the  latter  use  the  material  must  show  as  even  a 
surface  of  colour  as  possible,  and  therefore  must  be  free 
from  the  reversed  portions  due  to  twinning.  The  stone 
must  be  cut  too  with  the  exposed  surface  parallel  to  the  less 
perfect  cleavage  referred  to.  At  one  time  specimens  that 
showed  peculiar  distributions  of  colour,  which  by  a  little 
imagination  might  be  regarded  as  portraits,  were  in  great 
demand  and  high  prices  were  asked  for  them  ;  one  specimen 
is  recorded  to  have  shown  a  distinct  head  of  Louis  XVI., 
and  for  this  £10,000  was  asked  in  1799.  M.  de  Dree  had 
a  small  table,  the  top  of  which  was  composed  of  two  pieces 
of  Labradorite,  that  sold  for  £75. 


CHAPTER  XL 

325.    AUGITE. CEOCIDOLITE. 

AUGITE  is  one  of  a  group  of  minerals  known  by  the  group- 
name  of  Pyroxenes,  which  are  metasilicates  of  calcium, 
magnesium,  and  iron.  Of  the  numerous  varieties  of  Augite 
we  are  only  concerned  with  one,  Diopside,  and  the  description 
will  be  confined  to  that. 

Diopside,  which  is  also  known  as  Malacolite,  Alalite,  and 
Mussite,  occurs  in  green,  or  rarely  grey,  to  white  crystals 
usually  attached  in  groups  (Fig.  17).  The  tint  of  green 
varies  from  very  pale  to  very  dark.  The  crystals  are 
transparent  to  translucent,  and  of  a  high  vitreous  lustre. 
They  are  doubly  refracting,  but  show  only  very  slight 
dichroism,  even  in  the  specimens  possessing  a  deep  colour. 
The  specific  gravity  varies  from  3*2  to  3*4,  being  greater  in 
the  deeper  coloured  varieties.  Diopside  is  a  brittle  mineral. 
Its  hardness  is  equal  to  6,  and  it  has  a  well-marked  cleavage 
parallel  to  the  faces  of  the  rhombic  prism.  It  crystallises 
in  the  monosymmetric  system,  and  the  usual  habit  of  the 
crystal  is  prismatic,  with  a  well-marked  oblique  termination. 
The  prism  faces  are  striated  longitudinally.  The  prism  is 
composed  of  a  right-angled  form,  whose  solid  edges  are 
truncated  by  the  faces  of  the  rhombic  prism.  The  crystals 
are  always  attached  at  one  end,  and  are  often  in  groups. 
Twin  crystals  are  often  seen.  It  occurs  in  cavities,  with 


PEECIOUS  STONES.  219 

the  variety  of  Garnet  known  as  Hessonite,  and  with 
Mica.  In  chemical  composition  it  is  a  calcium  magne- 
sium metasilicate,  CaMg  (Si03)2,  usually  with  a  variable 
amount  of  iron,  that  with  the  greater  amount  being 
darker  in  colour  and  of  greater  density.  Diopside  was 
originally  found  at  the  Mussa  Alp,  in  the  Ala  valley  in 
Piedmont,  hence  the  names  Alalite  and  Mussite.  It  is  also 


FIG.  17. — Diopside. 

found  at  the  Schwarzenstein  Alp,  in  the  Tyrol,  and  at 
De  Kalb,  in  New  York  State.  When  cut  as  a  gem  the  clear 
green  transparent  forms  are  used,  and  they  are  either  step 
or  table  cut.  They  are  chiefly  used  in  the  countries  where 
the  mineral  is  found.  It  is  rather  difficult  to  distinguish 
from  Olivine,  but  Diopside  is  the  softer  mineral  of  the  two. 
The  green  Chrysoberyl  and  green  Idocrase  are  both  denser 
than  Diopside,  while  Tourmaline  and  Epidote  are  more 


220  PRECIOUS  STONES. 

strongly  dichroic.  Emerald  and  Dioptase  differ  from 
Diopside  in  colour.  A  glass  imitation  may  at  once  be 
known  by  the  single  refraction. 

327.  SPODUMENE. 

Spodumene  is  another  mineral  belonging  to  the  Pyroxene 
group,  but  until  comparatively  recent  times  it  was  of  no 
importance  as  a  precious  stone.  However,  in  1879 
Mr.  W.  E.  Hidden  discovered  a  beautiful  variety,  which  has 
been  named  in  his  honour ;  and  more  recently  still  another 
variety  has  been  found  in  California,  and  named  by  Dr. 
Baskerville  after  Dr.  G.  F.  Kunz,  the  author  of  "  The 
Gems  and  Precious  Stones  of  North  America." 

The  colour  of  the  ordinary  variety  of  Spodumene  is  white, 
grey,  yellow,  or  rarely  somewhat  violet ;  Hiddenite  varies 
from  yellow-green  to  emerald-green,  and  it  is  from  specimens 
of  the  latter  colour  that  the  gem  stones  are  cut ;  Kunzite 
is  found  in  various  shades  of  pink,  violet,  and  blue.  The 
mineral  is  transparent  to  translucent,  the  lustre  is  vitreous. 
It  is  doubly  refracting,  the  greatest  and  least  indices  for 
the  D  line  being  1'68  and  1*65.  It  shows  strong  pleo- 
chroism,  and  the  variety  Kunzite  has  a  marked  phos- 
phorescence induced  by  exposure  to  X-rays  and  to  the 
emanations  of  radium.  The  specific  gravity  is  3*15  to  3*20, 
and  the  hardness  is  6j  to  7.  In  crystalline  form  it  is 
monosymmetric,  and  the  habit  is  usually  prismatic.  The 
crystals  show  vertical  striations,  and  Hiddenite  often  shows 
etched  markings.  There  is  a  perfect  cleavage  parallel  to 
the  prism  faces.  The  crystals  of  the  ordinary  variety  are 
often  very  large,  up  to  4  feet  long  and  1  foot  across.  Hid- 
denite occurs  in  slender  crystals  of  1^  to  2  inches  in  length. 


PKECIOUS  STONES.  221 

In  chemical  composition  Spodumene  is  a  lithium 
aluminium  metasilicate,  LiAl(Si03)2. 

Spodumene  is  usually  found  in  crystalline  rocks  that  have 
been  formed  under  great  pressure,  and  it  is  frequently 
associated  with  such  minerals  as  Tourmaline,  Magnetite, 
Beryl,  Garnet,  Monazite,  Mica,  and  Quartz. 

Two  rare  colours  of  the  ordinary  variety  from  Brazil 
have  been  found  suitable  for  gem  use.  One  is  greenish- 
yellow  and  transparent,  and  was  for  long  mistaken  for 
Chrysoberyl,  and  the  other  is  transparent  and  blue,  and 
is  found  near  Diamantina  in  Minas  Geraes,  and  was 
mistaken  for  Lazulite.  Greenish-yellow  transparent 
crystals  have  also  been  found  with  Hiddenite  in  the 
United  States. 

The  variety  Hiddenite  was  found  near  Stony  Point  in 
Alexander  County,  North  Carolina,  in  cavities  in  a  granitic 
rock.  There  was  a  great  demand  for  the  gem  in  the 
United  States,  and  the  supply  from  this  locality  soon 
became  exhausted.  In  value  the  gem  is  comparable  to  a 
good  Diamond. 

About  twenty  years  after  the  discovery  of  Hiddenite  the 
variety  Kunzite  was  found,  at  a  mine  in  the  Pala  mountains 
in  San  Diego  county,  California.  The  crystals,  apart  from 
their  beautiful  colour,  were  remarkable  for  their  size  and 
perfection,  and  the  cut  gem  soon  acquired  as  high  a  value 
as  almost  any  gem,  over  ^£200  being  asked  for  some 
specimens. 

Most  of  the  specimens  have  been  retained  privately  in 
America,  but  the  national  collection  in  the  British  Museum 
and  the  American  Natural  History  Museum  collection 
include  tine  specimens., 


222  PKECIOUS   STONES. 

Spodumene  may  be  distinguished  from  other  yellow-green 
minerals  which  are  doubly  refracting,  as  follows :  Beryl  is 
distinctly  less  dense,  Chrysoberyl  and  Olivine  are  distinctly 
more  dense,  and  Diopside  is  slightly  denser.  Beryl  and 
Chrysoberyl  are  harder.  Diopside  is  not  so  hard,  Olivine 
is  of  about  the  same  degree  of  hardness,  but  both  Olivine 
and  Diopside  are  less  markedly  dichroic  than  Spodumene, 
and  so  is  Emerald,  which  can  be  further  distinguished  from 
Hiddenite  by  the  Emerald  having  a  colour  more  pure  and 
intense.  Kunzite  and  Amethyst  may  be  of  nearly  equal 
hardness,  but  Amethyst  is  of  lower  specific  gravity,  and  is 
less  markedly  dichroic.  Oriental  Amethyst  (Corundum) 
while  strongly  dichroic,  is  very  much  denser  than  Kunzite, 
and  very  much  harder.  Various  colours  of  Garnet  and  all 
glass  imitations  may  be  distinguished  from  Spodumene  by 
their  single  refraction. 

328.  JADEITE. 

This  mineral,  which  is  really  one  of  the  Pyroxene  group, 
is  often,  with  its  variety  Chloromelanite  and  the  Amphibole 
mineral  Nephrite,  spoken  of  as  Jade  ;  thus  this  term  includes 
two  distinct  species  of  mineral. 

Jadeite  is  only  known  massive,  though  it  has  a  micro- 
scopical crystalline  structure,  and  is  supposed  to  be  either 
monosymmetric  or  triclinic.  The  masses  show  an  intimate 
fibrous  structure  which  renders  the  mineral  remarkably 
tough  and  hard  to  fashion.  In  colour  pure  specimens  are 
almost  white,  tinged  usually  with  apple-green  streaks ; 
sometimes  it  is  seen  of  an  emerald-green  colour  or  leek 
green.  It  is  translucent  to  sub-translucent  in  thin  pieces, 
and  in  the  mass  opaque.  The  lustre  is  sub-vitreous  to 


PBECIOUS   STONES.  223 

pearly.  Heat  readily  causes  it  to  fuse  to  a  glassy  mass. 
The  specific  gravity  is  3*33  to  3'35  ;  the  hardness  is  6j  to  7. 
Little  is  known  definitely  about  its  origin ;  it  is  said  to  be 
found  in  rolled  masses  in  a  clay  of  reddish  colour. 

In  chemical  composition  it  is  a  sodium  aluminium 
silicate,  NaAl(Si03)2.  The  variety  Chloromeianite  is  of  a 
dark  green  colour  and  contains  a  good  deal  of  iron. 

The  most  important  locality  for  Jadeite  is  in  Upper 
Burma,  on  the  Eiver  Uru,  where  it  occurs  massive  in 
situ  in  a  dark  serpentine,  and  also  in  boulders  in  the 
river  below.  Here  it  is  extensively  mined,  and  thence 
much  of  it  is  sent  to  China,  where,  with  the  other 
substance  known  as  Jade,  it  is  called  Yu  or  Yu-shih. 
Some  of  it  is  also  sent  to  Mandalay,  and  there  cut. 

Jadeite  is  also  said  to  occur  in  the  Yarkand  regions  in 
situ,  and  it  may  very  likely  be  found  in  situ  in  the  Alps,  as 
rough  unworked  fragments  are  found  around  the  Lakes 
Neuchatel  and  Geneva,  and  it  is  said  to  occur  in  Alaska. 

Ancient  implements  made  of  Jadeite  are  found  very 
widely  distributed  in  Europe,  Asia,  America  and  Africa. 

It  is  a  highly  prized  mineral  amongst  the  Chinese,  who 
fashion  it  into  rings,  vases,  cups,  and  numerous  other 
articles,  displaying  a  skill  and  patience  in  their  work  that 
is  truly  remarkable.  Many  prehistoric  weapons  are 
wrought  in  this  material,  and  the  ancient  Egyptians  made 
some  of  the  scarabs  of  it.  Good  specimens  still  command  a 
very  high  price,  especially  in  China. 

THE  AMPHIBOLE  GROUP. 

This  group,  like  the  Pyroxene  group,  comprises  several 
species  of  closely  allied  minerals,  amongst  which  only  two 


224  PKECIOUS   STONES. 

concern  us :  these  are  Nephrite,  a  variety  of  Hornblende, 
and  Crocidolite.  As  in  the  Pyroxene  group,  the  various 
members  of  the  Amphibole  group  show  forms  belonging  to 
different  crystallographic  systems  but  yet  closely  alike  in 
form.  Again  they  are  metasilicates  of  calcium,  magnesium 
and  iron,  but  in  this  instance  the  alkali  metals  are  more 
often  found  in  the  minerals  as  well. 

338.  HORNBLENDE  :    VARIETY  NEPHRITE. 

Although  this  species,  Hornblende,  is  sometimes  referred 
to  as  Amphibole,  it  seems  better  to  retain  the  latter  name 
as  the  name  of  the  group.  The  crystalline  varieties  of 
Hornblende  differ  so  widely  in  appearance  from  Nephrite 
that  it  must  suffice  to  say  the  crystals  are  of  the  monosym- 
metric  system,  show  a  generally  rather  slender  prismatic 
habit,  and  have  a  distinct  prismatic  cleavage.  There  is  a 
marked  pleochroism. 

Nephrite,  which  is  also  known  as  Axe-Stone  and  Kidney- 
Stone,  is  included  under  the  old  term  Jade  and  the  Chinese 
term  Yu.  It  is  never  found  in  crystals,  but  always  in  more 
or  less  irregular  masses  showing  an  intimate  fibrous 
structure  which  renders  it,  like  Jadeite,  particularly  tough, 
so  that  to  break  a  piece  of  any  size  with  a  hammer  is  no 
easy  matter.  In  colour  it  is  usually  greenish,  but  the 
colour  varies  a  good  deal  according  to  the  amount  of  iron 
present,  that  with  more  iron  showing  a  more  pronounced 
green.  Very  rarely  it  is  colourless,  or  tinted  with  red  or 
blue.  Nephrite  is  never  transparent,  and  is  only  trans- 
lucent in  thin  pieces.  The  specific  gravity  varies  from 
2'91  to  3'2,  but  as  a  rule  may  be  taken  as  3'0.  The  fracture 
js  splintery  and  the.  mineral  is  remarkably  tough;  the 


PRECIOUS  STONES.  225 

hardness  is  6  or  6J.  When  found  in  situ  it  is  always  in 
metamorphic  rocks  of  one  kind  or  another  ;  thus,  in  Ger- 
many it  occurs  at  Jordansmiihl  and  Eeichenstein  in  Silesia; 
in  Turkestan  it  occurs  on  the  Yarkand  Daria  below  Yarkand 
and  between  there  and  Khotan,  both  in  situ  and  as  water- 
worn  fragments  in  the  rivers,  also  further  east  on  the 
northern  slopes  of  the  Kuen-Lun  (Jan  Shanskii)  Mountains. 
Dr.  (jr.  F.  Kunz  records  the  finding  of  Nephrite  in  situ  in 
Siberia  by  members  of  the  Kussian  Geological  Survey,  in 
the  district  of  Chara  Jalga.  It  has  also  been  found  in  the 
rock  in  Alaska,  in  the  South  Island  of  New  Zealand  and  in 
various  parts  of  Polynesia.  Nephrite  has  also  been  found 
in  the  unworked  state,  but  not  in  situ,  in  the  glacial  deposits 
of  Northern  Germany,  in  the  district  of  Irkutsk  in  Siberia, 
in  the  above-mentioned  localities  in  Eastern  Turkestan  and 
in  the  west  of  the  Chinese  Empire,  in  New  Zealand  and  in 
Alaska  ;  also  on  the  Eraser  Kiver  in  British  Columbia. 
In  Switzerland,  Germany,  Mexico,  and  New  Zealand, 
Nephrite  was  used  in  very  remote  times  for  battle-axes  and 
other  weapons,  and  it  is  supposed  the  Chinese  have  worked 
the  deposits  in  the  Kuen-Lun  Mountains  for  2,000  years, 
using  the  material  in  the  same  way  as  Jadeite  and  other 
stones  known  to  them  as  Yu.  When  used  among  Western 
nations  it  is  usually  in  the  form  of  a  ring  cut  from  the  solid 
material,  or  for  small  pieces  (en  cabochon)  for  setting  in 
brooches,  etc. 

Nephrite  is  most  likely  to  be  confused  with  Jadeite,  but 
the  latter  is  distinctly  denser  as  a  rule,  though  occasionally 
specimens  of  Jadeite  are  found  with  a  specific  gravity  included 
in  the  range  Nephrite  shows.  The  value  of  well  worked 
ornaments  in  Nephrite  is  high  on  account  of  the  great  time 

p.s.  Q 


OF  THE 

UNIVERSITY 


226  PRECIOUS   STONES. 

required  to  execute  the  work,  and  amongst  the  Chinese  the 
rough  material  is  greatly  sought  after  and  commands  a 
high  price. 

341.  CROCIDOLITE. 

Crocidolite  is  another  member  of  the  Amphibole  group 
and  is  of  interest  in  that  it  gives  the  characteristic  appear- 
ance to  the  precious  stones  known  as  Hawk's  Eye  and 
Tiger's  Eye,  though  both  of  these  are  in  a  greater  or  lesser 
degree  alteration  products  of  Crocidolite. 

Crocidolite  occurs  in  narrow  veins  or  bands  having  a 
transverse  closely  fibrous  structure  due  to  the  parallel 
arrangement  of  numerous  minute  acicular  crystalline 
growths.  The  colour  of  the  unaltered  mineral  is  a  leek 
green.  The  lustre  of  one  of  these  fibrous  pieces,  even  when 
broken,  is  distinctly  silky.  On  heating,  a  little  water  is 
driven  off,  and  the  mineral  then  easily  fuses.  The  specific 
gravity  is  8*2  to  3'3,  but,  as  will  be  seen  below,  the  specific 
gravity  of  the  two  varieties  mentioned  may  fall  to  nearly 
that  of  Quartz.  The  hardness  of  Crocidolite  is  4. 

In  composition  it  is  a  sodium  ferri-ferrous  metasilicate, 
NaFe  (Si03)2,  FeSi03.  Infiltration  of  this  fibrous  mineral 
with  Quartz  gives  the  variety  Hawk's  Eye,  of  a  blue 
green  to  indigo  blue  colour ;  the  process  of  infiltration  is  a 
gradual  one,  so  all  stages  are  found  between  what  is  an 
undoubted  Amphibole  and  a  substance  which  may  be 
regarded  as  a  variety  of  Quartz  showing  inclusions. 
Further  by  a  gradual  change  the  Crocidolite  may  be  decom- 
posed, its  iron  passing  into  the  state  of  the  hydrate  (Limonite) 
and  the  silica  remaining,  with  possibly  addition  of  silica 
from  outside,  as  Quartz,  and  thus  the  golden  brown  stone 


PRECIOUS  STONES.  227 

known  as  Tiger's  Eye  is  produced  ;  it  may  also  be  regarded 
as  a  form  of  Quartz  containing  pseudomorphs  of  Crocidolite 
in  Limonite.  The  Hawk's  Eye  may  thus  show  a  transition 
to  Tiger's  Eye ;  hence  the  only  definite  starting  point  we 
have  in  tracing  the  origin  of  these  two  precious  stones  is 
the  original  Crocidolite,  and  for  this  reason  they  are 
described  under  this  species.  It  follows,  from  what  has 
been  said,  that  when  the  infiltration  by  Quartz  is  complete 
the  specific  gravity  is  that  of  Quartz  with  a  slight  excess 
due  to  the  inclusions,  and  further  the  hardness  is  7. 

Tiger's  Eye  and  Hawk's  Eye  both  occur  in  veins  in 
schists  in  the  Asbestos  Mountains  in  Griqualand  West, 
and  in  other  parts  of  South  Africa. 

At  one  time  the  material  was  scarce  and  was  only  used 
for  smaller  articles  of  ornament,  but  now  there  is  a  plentiful 
supply  and  the  price  has  fallen  so  much  that  it  is  commonly 
used  for  paper  weights,  umbrella  handles,  and  other  similar 
articles.  The  variety  Tiger's  Eye  when  polished  with  the 
exposed  surface  parallel  to  the  fibres  had  a  particularly 
brilliant  golden  brown  colour  and  shows  a  highly  silky 
lustre. 


CHAPTER  XII. 

344.    BERYL GARNET. 

BERYL  is  one  of  the  gem  stones  that  has  been  known  from 
ancient  times.  The  term  Smaragdus  of  the  old  writers 
included  Beryl  and  its  green  varieties  amongst  many  other 
green  stones,  and  Pliny's  Beryllus  was  almost  certainly  this 
mineral.  It  is  probable  that  the  Beryl  of  Aaron's  Pectoral 
was  also  our  Beryl.  Pliny  further  mentions  that  the  gem 
came  solely  from  India,  and  that  the  blue-green  kind 
(Aquamarine)  was  the  most  prized.  The  name  is  said  to  be 
derived  from  a  Low  Latin  word  meaning  a  lens,  possibly  on 
account  of  the  Romans  cutting  their  transparent  gems  with 
curved  surfaces  in  many  cases,  though  they  are  reputed  to 
have  cut  the  Beryl  in  the  form  of  a  low  six-sided  pyramid, 
guided  possibly  by  the  natural  form  of  the  crystal  termina- 
tion. It  was  reputed  to  be  a  cure  for  diseases  of  the  eye, 
possibly  on  account  of  the  well-known  soothing  effect  of 
green  light.  It  would  appear  that  someone,  endowed  with 
a  more  exact  power  of  reasoning  than  many  of  his  con- 
temporaries, who  was  wearing  an  Emerald  or  Beryl  on 
account  of  its  reputed  value  in  eye  affections,  found  that 
he  could  really  see  better  with  his  Beryllus,  which  was 
probably  cut  with  two  curved  surfaces  so  as  to  be  a 
meniscus,  thinner  in  the  centre  than  at  its  periphery,  and 
rightly  attributed  the  effect  to  the  shape  of  the  stone 
and  not  to  its  kind,  and  thus  led  to  the  correction  of 


PKECIOUS  STONES.  229 

myopia  by  means  of  concave  lenses.  It  is  also  said  by 
Pliny  that  Nero  watched  the  gladiators  fight,  aiding  his 
sight  by  an  eye-glass  of  Emerald. 

It  was  much  used  by  the  Eomans  for  ear  drops,  and  was 
sometimes  engraved  by  them,  though  rarely,  as  they  held 
it  in  too  high  an  esteem  to  be  used  .often  as  material  for 
intagli.  The  Indians,  too,  pierced  the  commoner  varieties, 
and  used  them  as  elongated  beads,  while  the  more'precious 
kinds  were  mounted  in  gold  in  their  natural  state,  and  worn 
as  pendants  in  very  much  the  same  way  as  crystals  have 
been  used  quite  recently. 

Beryl  is  found  in  a  variety  of  colours,  and  different  terms 
are  applied  to  the  gem  according  to  the  colour. 

Emerald  includes  the  bright  green  shade  which  is  so 
well  known  that  this  particular  colour  is  constantly  spoken 
of  as  emerald-green.  Aquamarine  covers  the  pale  blue, 
bluish-green,  and  greenish-blue  shades  of  Beryl  ;  the 
yellow-green  shade  is  Aquamarine-Chrysolite,  and  the 
bright  yellow  is  Golden  Beryl  ;  these  three  together  are 
known  as  Precious  Beryl.  Other  colour  shades  include  : 
a  pale  yellow-green,  which  may  have  been  the  Chrysoprasius 
and  Chrysoberyllus  of  Pliny,  in  part,  at  least ;  the  apple 
green,  pale  rose  red,  rarely  a  sapphire  blue,  and  a  pale 
violet.  Sometimes  Beryl  is  found  colourless. 

The  mineral  occurs  from  transparent  to  subtranslucent, 
but  the  modern  gem  varieties  are  confined  to  the  transparent 
kinds.  The  lustre  is  characteristically  vitreous.  Double 
refraction  is  only  feeble,  the  index  for  the  ordinary  ray 
being  1*584,  and  for  the  extraordinary  T578;  and  the  dis- 
persion is  small,  hence  there  is  but  little  play  of  colour  due 
to  refraction.  The  mineral  is,  however,  distinctly  dichroic, 


230  PEECIOUS  STONES. 

and  the  difference  in  colour  in  the  various  directions  may 
sometimes  be  seen  without  the  aid  of  the  dichroscope. 
The  green  colour  of  the  Emerald  is  not  discharged  by 
strongly  heating,  hence  is  not  due  to  organic  matter. 
Before  the  blowpipe  even  thin  splinters  fuse  with  difficulty, 
first  turning  an  opaque  white. 

The  specific  gravity  of  Beryl  is  2'67  to  2'75.     The  fracture 
is  conchoidal,  and  the  mineral  is    distinctly  brittle,   and 


FIG.  18.  FIG.  19. 

Crystals  of  Beryl. 

hence  must  be  handled  with  care.  The  hardness  is  7  j  to  8. 
There  is  an  indistinct  cleavage  parallel  to  the  basal  plane. 
The  streak  is  white. 

In  crystalline  form  it  is  hexagonal,  and  the  crystals 
usually  show  a  rather  slender  prismatic  habit  (Fig.  18),  and 
are  often  striated  vertically  by  repeated  oscillations  of 
different  prism  faces.  The  Emerald  in  particular  is  very 
frequently  seen  to  have  numerous  minute  internal  cracks 
and  fissures,  so  that  "  an  Emerald  without  a  flaw  "  is  quite 


PRECIOUS  STONES.  231 

proverbial.  The  crystals  as  a  rule  show  a  prominent 
hexagonal  prism,  with  the  dihedral  angles  modified  by  a 
narrower  face  belonging  to  another  prism  (Fig.  19). 
Terminated  crystals  are  rather  the  exception,  but  when 
they  do  occur  the  form  of  the  termination  is  often  very 
complex.  More  often  the  prism  is  limited  by  an  eroded 


FIG.  20. — Emerald  in  its  Matrix. 

surface  (Fig.  20)  (cf.  Tourmaline).  Another  not  uncommon 
feature  is  the  transverse  separation  along  the  cleavage 
planes,  with  displacement  of  the  fragments  and  subsequent 
cementation  by  Quartz.  Attached  crystals  are  often  found 
in  Druses  in  certain  granites  ;  most  of  the  clear  terminated 
crystals  are  so  found.  Another  common  mode  of  occurrence 


232  PKECIOUS   STONES. 

is  in  pegmatitic  rocks  which  have  been  formed  by  dynamo- 
metamorphism,  and  to  this  group  belong  most  of  the 
crystals  showing  dislocation  and  absorption,  and  many  of 
the  more  opaque  varieties. 

Beryl  is  a  metasilicate  of  aluminium  and  beryllium,  the 
latter  element  being  so  called  from  its  presence  in  Beryl. 
Emerald  probably  owes  its  beautiful  colour  to  the  presence 
of  traces  of  chromium  ;  many  specimens  of  Beryl  contain  a 
little  iron  and  calcium  as  well  but  they  do  not  seem  to 
be  in  any  way  essential,  so  the  formula  may  be  expressed 
as  3  BeO,  A1203,  6  Si02.  Many  specimens  also  contain 
1  per  cent,  to  2  per  cent,  of  chemically  combined  water. 
Beryl  resists  the  action  of  all  acids  except  hydrofluoric 
acid,  by  which  it  is  attacked. 

The  distribution  of  Beryl  is  very  wide.  Probably  the 
locality  which,  as  far  as  is  known,  is  the  oldest  is  one  in 
Egypt,  where  Emerald  is  believed  to  have  been  mined 
1650  B.C.,  if  not  earlier.  The  crystals  occur  in  mica-schist 
at  Jebel  Sikait  and  Jebel  Sabara ;  they  are  of  a  good 
colour,  but  rather  pale. 

It  is  very  doubtful  if  the  Emerald  really  came  from  India 
in  Pliny's  time  ;  certainly  there  is  no  authentic  record  of  it 
having  been  found  there,  though  other  shades  of  Beryl,  as 
the  pale  blue  Aquamarine,  occur  in  pegmatite  bands  in 
gneiss  in  the  Punjab  and  in  other  parts  of  India.  Many 
of  the  crystals  are  of  large  size,  but  are  not  of  very  good 
quality,  being  extensively  fractured. 

Peru  was  for  a  long  time  believed  to  be  the  home  of  the 
Emerald ;  the  Spaniards  undoubtedly  brought  large  numbers 
of  this  gem  from  Peru  in  the  sixteenth  century ;  and  it  is 
recorded  in  "Ceremonies  Eeligieuses"  that,  before  the  time  of 


PKECIOUS  STONES.  233 

the  Incas,  the  Peruvians  used  as  an  idol  an  Emerald  as  large 
as  an  ostrich  egg,  which  the  priests  explained  was  the 
mother-emerald  who  liked  daughters,  and  thus  induced  her 
worshippers  to  offer  "daughter-emeralds"  to  the  goddess, 
much  to  the  enrichment  of  the  Spanish  when  they  con- 
quered the  country.  Certain  it  is  that,  in  spite  of  most 
careful  search  by  the  Spanish  and  by  later  explorers,  no 


FIG.  21.— Emerald  in  the  Matrix  (Colombia). 

trace  of  the  Emerald  has  been  found  in  Peru.  Still,  the 
fact  that  such  beautiful  specimens  were  brought  to  Europe 
by  the  Spanish  from  Peru  has  given  us  the  terms  "  Spanish 
Emerald  "  and  "  Peruvian  Emerald,"  as  indicating  Emeralds 
of  the  finest  quality. 

The  Spaniards,  however,  found  Emeralds  in  New 
Granada  (Colombia),  and  the  deposits  there  have  been 
worked  intermittently  ever  since  and  have  provided  some 


234  PEECIOUS   STONES. 

of  the  finest  specimens  known.  The  place  where  they  were 
first  worked  by  Europeans,  and  whence  they  had  been  pre- 
viously obtained  by  the  natives,  was  at  Somondoco  on  the 
eastern  slopes  of  the  Cordillera  of  Bogota  ;  these  deposits, 
though  still  sometimes  worked,  do  not  yield  very  fine  quality 
stones.  Afterwards  another  deposit  was  found  on  the 
western  slopes  of  the  Eastern  Cordillera  to  the  east  of  the 
Kio  Magdalena  and  near  the  town  of  Muzo,  lying  to  the 
north  of  the  capital,  Bogota.  This  is  now  the  principal 
locality  in  which  the  gem  is  found  ;  the  mineral  occurs  in 
a  dark  bituminous  limestone,  and  the  crystals  are  usually 
implanted  on  Calcite,  the  latter  occurring  in  cavities  in  the 
limestone  (Fig.  21).  This  deposit  is  of  interest  in  another 
way,  because  it  practically  forms  the  only  exception  to  the 
rule  that  Emerald  occurs  in  granitic  and  dynamo-meta- 
morphic  rocks.  The  associates  are  exceptional  also,  Gypsum, 
Pearlspar,  Quartz,  Iron  Pyrites,  and  a  rare  mineral  called 
Parisite  being  found  with  the  Emerald.  Many  of  the 
specimens  show  the  dislocations,  but  in  this  case  the 
material  filling  the  fissures  is  Calcite  and  not  Quartz.  The 
stones,  too,  are  prone  to  become  turbid  after  a  time  from 
the  formation  of  numerous  minute  flaws.  Emeralds  of 
gem  quality  are  known  locally  as  Canutillos,  and  those  not 
fit  for  cutting  as  Morallons. 

Also  in  South  America,  in  Brazil,  Beryl  occurs  in  some 
quantity  in  the  north-east  of  Minas  Geraes,  associated  with 
Topaz  and  Chrysoberyl  ;  the  crystals  are  often  of  several 
pounds  weight,  but  the  larger  ones  are  usually,  as  else- 
where, cloudy  and  in  a  large  part  unfit  to  cut.  The 
mineral  here  is  probably  derived  from  a  granitic  rock. 
Near  Rio  de  Janeiro,  too,  Beryl  occurs  in  pegmatite  bands 


PRECIOUS  STONES.  235 

in  gneiss.  The  variety  Aquamarine-Chrysolite  is  found  in 
Brazil. 

In  North  America,  Emerald  is  found  at  Stony  Point  in 
Alexander  County,  North  Carolina,  with  Hiddenite  ;  other 
forms  of  Beryl  also  occur  here.  Eussel  Gap  Eoad,  also  in 
Alexander  County,  is  a  good  locality  for  Aquamarine.  In 
Maine,  in  Oxford  County,  green  Beryl  is  found,  and  at 
Albany  Golden  Beryl  occurs.  At  Eoyalston  in  Massa- 
chusetts, Beryl  of  a  sapphire  blue  is  found.  At  Graf  ton  in 
Hampshire,  a  large  Beryl  crystal  was  found  which  weighed 
2£  tons.  Emerald  also  occurs  at  Haddam  in  Connecticut. 
In  Colorado,  on  Mount  Antero  very  fine  Aquamarines  are 
found,  associated  with  Phenakite. 

In  the  Ural  Mountains  Beryl  is  found  at  many  places ; 
thus  in  the  Ekaterinburg  district  it  is  found  at  Mursinka 
and  Shaitanka  in  cavities  in  pegmatitic  rock.  The  variety 
Aquamarine-Chrysolite  occurs  here  as  well  as  Beryl  of 
other  shades,  as  various  greens  and  yellows.  The  crystals 
are  smooth  and  are  associated  with  Topaz,  Felspar,  Tour- 
maline and  Quartz.  To  the  east  of  Ekaterinburg  Emerald 
occurs  in  mica-schist  with  Chrysoberyl,  Kutile,  Phenakite, 
Apatite,  and  Fluor  Spar.  The  crystals,  which  are  often 
large,  are  in  many  cases  poor,  show  dislocations,  and  are 
rarely  terminated. 

In  the  Ilmen  Mountains  pale  green  Beryl  is  found  in 
pegmatite  with  Topaz  and  Amazon  stone,  and  large  crystals 
occur  in  the  Altai  Mountains.  In  the  Nerchinsk  district 
Beryl  is  found  in  the  Adun-Chalon  Mountains  in  pegmatite 
bands  in  granite  with  Topaz  and  Quartz,  with  over  all  a 
layer  of  Limonite  (Fig.  22).  Also  on  the  Urulga  Eiver  in 
fine  yellow-green  crystals, 


236  PEECIOUS  STONES. 

Emerald  has  been  found  in  the  Salzburg  Alps  at  Sedlalp, 
with  Tourmaline  and  Iron  Pyrites  in  mica-schist.  In  the 
Mourne  Mountains  in  Ireland  Beryl  is  found  with  Quartz, 
Felspar  and  Topaz,  in  druses  in  the  granite. 

In  Australia,  in  New  South  Wales,  at  Emmaville, 
Emerald  occurs  in  pegmatite  with  unusual  associates,  as 


FIG.  22. — Beryl  Crystals,  partly  coated  with 
Limonite. 

Cassiterite,  Mispickel  and  Fluor  Spar,  and  the  more  usual 
associate  Topaz. 

Fine  varieties  of  Beryl  are  sometimes  brilliant  cut,  the 
deeper  coloured  specimens  requiring  a  rather  shallow  form, 
while  the  paler  shades  must  be  given  a  good  depth  to 
ensure  a  fine  colour  effect.  More  often  a  mixed  cut  is  used, 
or  a  pure- step  cut.  Good  stones  with  fine  colour  may  be 
mounted  d  jour,  but  stones  of  poorer  colour  are  often 
improved  by  being  mounted  with  foil  in  a  closed  setting. 


PRECIOUS  STONES.  237 

In  value  an  Emerald  of  best  quality  ranks  nearly  as  high 
as  the  Kuby,  a  perfect  stone  of  one  carat  often  selling  for  £20 ; 
owing  to  the  difficulty  of  obtaining  Emeralds  without 
imperfections  in  the  larger  sizes,  the  value  of  flawless 
stones  increases  very  rapidly  with  size.  Besides  the 
frequently  occurring  flaws  Emeralds  often  show  inclusions, 
rendering  the  stone  "  mossy."  The  colour  too  may  be 
irregularly  distributed ;  sometimes  only  the  extremity  of  a 
crystal  is  transparent.  A  fissured  stone  only  increases  in 
value  in  proportion  to  its  size,  and  it  may  be  worth  about 
£2  10s.  per  carat.  The  other  varieties  of  Beryl  are  often 
found  in  considerable  quantity  and  in  large  pieces,  hence 
the  value  is  much  lower  and  varies  very  closely  with  the 
weight. 

There  are  numerous  famous  specimens  of  Emerald  ;  two 
well  known  ones  may  be  instanced :  the  Czar's  Emerald, 
which  measures  ten  inches  in  length  and  five  in  diameter, 
and  the  Emerald  belonging  to  the  Duke  of  Devonshire, 
which  weighs  1,350  carats,  and  is  an  almost  perfect 
specimen. 

Owing  to  the  range  of  colour  shown  by  Beryl,  there  are 
a  number  of  minerals  which  may  have  to  be  distinguished 
from  it.  Of  these,  all  but  Quartz  are  more  dense.  Yellow 
Quartz  may  be  mistaken  for  Golden  Beryl,  but  the  Quartz 
is  lighter  and  also  shows  less  dichroism  and  is  rather 
softer.  Of  the  remainder,  green  Corundum  may  have  to 
be  distinguished  from  Emerald,  yellow  Corundum  from 
yellow  Beryl,  and  pale  blue  Corundum  from  Aquamarine. 
The  Corundum  is  denser  and  of  greater  hardness.  Green 
and  pale  blue  Tourmaline  may  similarly  be  distinguished 
from  Emerald  and  Aquamarine  respectively  by  their  greater 


238  PRECIOUS  STONES. 

density,  and  Tourmaline  is  never  quite  the  same  green  as 
Emerald,  usually  showing  a  trace  of  blue.  Topaz  in  its 
blue  and  yellow  shades  is  also  distinguished  by  a  higher 
specific  gravity  ;  the  same  holds  true  with  green  and  yellow 
Olivine,  and  in  addition  the  green  of  the  Olivine  is  rather 
yellow  and  the  mineral  is  only  feebly  dichroic,  Emerald 
showing  a  distinct  difference  in  the  two  images  under  the 
dichroscope,  one  image  usually  being  a  yellow-green  and 
the  other  a  blue -green.  Chrysoberyl  in  its  variety 
Alexandrite  is  more  strongly  dichroic,  is  harder,  and  is 
denser  than  Emerald.  Hiddenite,  a  variety  of  Spodumene, 
is  denser.  Dioptase  and  Diopside  are  of  a  rather  different 
colour,  the  former  of  a  deeper  tint  of  green  and  the  latter 
rather  more  of  a  glass  green ;  both  are  heavier  than 
Emerald,  and  Dioptase  is  also  softer.  Garnet  is  denser 
and  is  only  singly  refracting.  Euclase  is  denser  than 
Aquamarine.  Aquamarine  usually  shows  images  of  a  very 
pale  yellow -green  and  a  pale  blue-green  under  the 
dichroscope.  Glass  in  all  cases  is  softer,  and  is  moreover 
only  singly  refracting. 

353.   COKDIERITE. 

This  mineral  is  also  known,  from  its  strong  dichroism,  as 
Dichroite ;  it  is  frequently  called  lolite,  the  "  violet- 
stone."  The  colour  is  characteristically  some  shade  of 
blue,  but  on  account  of  the  marked  dichroism  the  colour 
varies  greatly,  even  in  a  given  specimen.  Thus  a  crystal 
from  Arendal,  in  Norway,  appeared  dark  blue  when  viewed 
along  the  longer  horizontal  axis  of  the  crystal,  a  light 
blue  along  the  shorter  horizontal  axis,  and  a  yellowish 
white  along  the  vertical  axis.  It  is  thus  more  correctly 


PRECIOUS  STONES.  239 

spoken  of  as  pleochroic.  It  is  transparent  to  translucent, 
and  has  a  vitreous  lustre  on  the  crystal  faces.  It  is  doubly 
refracting,  the  greatest  index  for  yellow  light  being  1*543, 
and  the  least  1*537.  The  dispersion  is  feeble.  It  is  only 
fusible  at  high  temperatures,  and  it  is  but  slightly  attacked 
by  acids.  The  specific  gravity  varies  from  2*60  to  2*72, 
depending  largely  on  the  amount  of  iron  present.  It  has  a 
conchoidal  fracture,  and  a  hardness  of  7  to  1\.  It  has  a 
distinct  cleavage  normal  to  the  longer  horizontal  axis,  and 
indistinct  cleavages  parallel  to  the  other  two  axes.  In 
crystalline  form  it  is  rhombic,  but  distinct  crystals  of  any 
size  are  rare,  and  when  they  are  found  are  usually  rough. 
The  general  habit  of  the  crystal  is  prismatic,  and  rather 
short.  Twinned  crystals  sometimes  give  rise  to  a  pseudo- 
hexagonal  form  (see  Chrysoberyl).  More  often  the  mineral 
occurs  in  rolled  fragments  or  massive.  Occasionally  com- 
pletely developed  crystals  are  found  in  granite,  as  in 
Bavaria,  but  usually  it  is  only  found  in  association  with 
rocks  which  have  undergone  great  metamorphism. 

In  chemical  composition  it  is  a  silicate  of  aluminium, 
with  magnesium  and  iron,  and  often  with  calcium,  and 
containing  water.  The  formula  is  possibly  H20, 4  (Mg,  FeO) , 
4  A1203,  10  Si02.  The  colour  is  probably  due  to  ferrous 
iron.  The  most  commonly  associated  minerals  are  Quartz, 
Orthoclase  or  Albite,  Tourmaline,  Garnet,  Andalusite, 
Beryl,  Topaz,  etc.  It  occurs  in  many  parts  of  Scandinavia, 
as  at  Arendal  and  Kragero  in  Norway ;  at  Abo  in  Finland ; 
at  Tunaberg  in  Sweden ;  in  Greenland,  etc.  But  the  chief 
gem  qualities  come  from  the  gem  gravels  of  Ceylon ;  there 
stones  of  both  light  and  dark  blue  are  found,  specimens  of 
a  sky  blue  being  known  as  Water  Sapphire  or  Saphir  d'Eau, 


240  PBECIOUS  STONES. 

while  the  darker  indigo  blue  stones  are  called  Lynx  Sapphire. 
Fine  specimens  have  been  found  at  Haddam  in  Connecticut, 
in  gneiss,  associated  with  Tourmaline.  The  gem  must  be 
cut  with  the  large  exposed  face  parallel  to  the  most  perfect 
cleavage  plane  to  bring  out  the  best  colour.  It  is  usually 
step  cut  or  table  cut,  but  a  variety  showing  asterism  is  cut 
en  cabochon ;  and  sometimes  the  mineral  is  cut  in  cubes, 
with  the  surfaces  normal  to  the  three  axes  of  the  crystal,  to 
show  the  pleochroism.  Its  low  specific  gravity  is  usually 
sufficient  to  distinguish  it  from  other  blue  stones,  but  in 
addition  the  strong  pleochroism  is  of  aid. 

365.  LAPIS  LAZULI. 

Lapis  Lazuli  is  only  to  be  regarded  as  a  mineral  in  so 
far  as  its  beautiful  colour,  on  which  its  use  as  a  precious 
stone  depends,  is  due  to  the  presence  of  a  disseminated 
mineral  in  a  matrix.  The  term  Lapis  Lazuli  thus  refers 
rather  to  a  rock,  and  the  colouring  mineral  is  now  more 
often  known  scientifically  as  Lazurite.  Nor  is  Lazurite  the 
only  coloured  mineral  present,  for  it  has  been  shown  that 
two  other  blue  minerals,  Haiiyne  and  Sodalite,  may  also  be 
in  the  matrix,  as  well  as  several  substances  whose  colour 
does  not  affect  the  whole  so  much.  Lapis  Lazuli,  which  is 
also  known  as  Azure  Stone,  was  almost  certainly  the 
Sapphirus  of  Theophrastus  and  other  ancient  writers.  It 
has  been  known  from  very  remote  times,  being  much  used 
by  the  Egyptians,  and  to  a  lesser  extent  by  the  Assyrians. 
Epiphanius,  Bishop  of  Salamis,  says  the  Tables  of  the 
Law  given  to  Moses  were  inscribed  on  Lapis  Lazuli. 
The  Komans  used  it  to  some  extent  as  a  material  for 
engraving  on. 


PKECIOUS  STONES.  241 

Lazurite  is  practically  always  of  a  blue  colour,  the 
commonest  shade  being  an  azure  blue,  sometimes  Berlin- 
blue,  rarely  of  a  violet  tinge,  sometimes  greenish  blue. 
Darker  parts,  merging  to  an  indigo  blue,  are  seen,  and 
often  white  streaks  and  yellow  metallic  patches,  due 
respectively  to  admixtures  of  Calcite  and  Iron  Pyrites.  As 
with  other  precious  stones,  the  richer  coloured  kinds  are 
known  as  "  masculine,"  and  the  paler  ones  as  "  feminine." 
It  is  translucent  to  opaque.  The  streak  is  ultramarine. 
On  heating  to  a  dull  red  the  pale  blue  shades  are  rather 
improved,  for  they  often  turn  to  a  richer  and  deeper  blue 
colour.  But  sometimes  the  effect  of  heating  is  to  make  the 
mineral  greenish  blue.  At  a  higher  temperature  the  blue 
colour  is  completely  discharged,  and  the  mineral  finally 
fuses  to  a  colourless  glassy  mass.  The  specific  gravity 
varies  from  2'38  to  2'45,  hence  it  is  one  of  the  lightest 
precious  stones.  The  fracture  is  uneven.  The  hardness  is 
5  to  5J.  The  crystalline  form  is  cubic,  but  it  is  very 
rarely  that  crystals  are  seen.  When  they  are  found  they 
are  small,  and  in  the  form  of  the  dodecahedron,  parallel  to 
the  faces  of  which  there  is  an  imperfect  cleavage.  The 
substance  known  as  Lapis  Lazuli  is  really  a  mass  of  fine 
particles  of  this  mineral,  along  with  several  others,  in  most 
cases  embedded  in  Calcite.  It  is  nearly  always  found  in 
limestones  that  have  been  subjected  to  extensive  meta- 
morphism,  either  by  proximity  to  a  great  plutonic  mass  or 
by  dynamic  changes.  The  chemical  composition  is  com- 
plex, and  by  no  means  invariable ;  it  may  be  expressed  as 
essentially  3  Na20,  3  A1203,  6  Si02,  2  Na2S3— a  sodium 
aluminium  silicate  with  sodium  sulphide.  It  is  of  some 
interest  to  note  that  Epiphanius  recommends  the  use  of 

p.s.  B 


242  PEECIOUS  STONES. 

powdered  Lapis  Lazuli  as  a  dressing  for  pustules  and 
boils,  for  it  is  possible  it  may  have  some  antiseptic  action 
when  moistened.  Since  the  mineral  is  imbedded  in  the 
carbonate  of  calcium,  Calcite,  it  follows  that  on  applying 
hydrochloric  acid,  effervescence  is  produced.  Also  the 
presence  of  the  sulphide  of  iron  would  render  it  liable  to 
decomposition  if  not  kept  dry.  With  regard  to  distribution, 
it  seems  more  than  likely  that  the  localities  mentioned  by 
the  old  writers  (Medea  and  Ethiopia)  may  have  simply  been 
trading  localities,  and  not  places  where  the  stone  was 
actually  to  be  found.  On  the  upper  part  of  the  river  Oxus, 
to  the  north  of  the  Hindu  Kush,  it  is  found  in  a  limestone 
rock,  and  here  it  has  been  worked  from  very  ancient  times, 
and  the  method  still  adopted  of  winning  it  seems  the  same 
as  it  was  then,  namely,  by  heating  the  rock  by  a  fire  and 
then  suddenly  cooling  it  with  water,  and  thus  causing  the 
rock  to  split  up.  Much  of  the  Lapis  Lazuli  from  this 
locality  goes  to  the  great  annual  fair  at  Nizhni  Novgorod, 
in  Russia. 

At  the  western  extremity  of  Lake  Baikal  it  occurs  to  the 
south  of  Kultuk  in  a  crystalline  limestone  near  the  meeting 
zone  of  granite  and  gneiss  ;  and  to  the  west  of  Kultuk  in  a 
granular  limestone  in  granite  a  good  deposit  exists ;  and 
here  an  improvement  in  quality  of  the  material  is  observed 
as  the  depth  of  the  workings  increases,  so  that  the  rich 
colour  is  probably  not  due  to  the  effect  of  weathering.  In 
the  Andes,  in  Chile,  it  occurs  in  a  metamorphosed  limestone 
underlying  a  granite  rock,  and  in  the  detritus  of  these  rocks. 
It  is  associated  with  Ruby  in  Burma. 

It  is  cut  as  a  flat  plaque,  or  en  cabochon ;  more  often  it 
is  worked  into  vases  and  other  small  ornamental  objects, 


PEECIOUS  STONES.  243 

though  now  the  solid  material  is  not  so  often  used  as  thin 
slices,  which  are  veneered  on.  It  is  largely  used,  too,  for 
mosaics  and  in  the  ornamentation  of  luxurious  buildings 
such  as  the  palaces  of  the  Russian  Czars.  Formerly  it  was 
the  sole  source  of  the  beautiful  pigment  ultramarine,  which 
was  greatly  esteemed  on  account  of  the  purity  of  its  colour 
and  permanence.  Now,  however,  the  pigment  is  made 
artificially,  though  the  artificial  product  does  not  command 
nearly  the  same  price.  All  the  substances  that  Lapis 
Lazuli  is  likely  to  be  mistaken  for  are  of  a  higher  specific 
gravity.  Stained  Agate  is  also  harder,  and  the  carbonate 
of  copper,  Azurite,  is  softer. 

870.  GARNET. 

The  term  Garnet  includes  a  series  of  isomorphous 
compounds,  all  of  which  have,  besides  a  very  closely  related 
chemical  composition,  very  similar  physical  properties. 

The  name  seems  to  have  been  derived  from  "  Grenat," 
which  really  referred  to  Hyacinth,  a  variety  of  Zircon.  It 
was  known  in  ancient  times,  for  Theophrastus  describes  a 
mineral,  that  was  almost  certainly  Garnet,  as  being  used  for 
mirrors.  The  "  feminine  Carbunculus  "  of  Pliny  probably 
included  some  of  the  Garnets,  his  Amethystizontes  being 
probably  Almandine  Garnets. 

The  predominant  colour  of  Garnet  is  some  shade  of  red, 
but  amongst  the  various  kinds  of  the  mineral,  yellow, 
green,  purple  and  brown  are  seen,  and  some  are  colourless 
and  some  are  black  ;  blue  is  never  seen.  The  colours  will 
be  more  particularly  referred  to  when  dealing  with  each 
kind  separately ;  the  lustre  varies  from  a  brilliant  vitreous 
lustre  to  a  resinous;  transparent  to  opaque;  normally  singly 

R  2 


244  PRECIOUS   STONES. 

refracting,  hence  not  showing  dichroism.  The  refractive 
index  for  yellow  light  varies  from  1'747  to  1'814 ;  the 
dispersion  is  small  in  all  except  Demantoid.  Almandine 
shows  absorption  bands  in  the  spectrum ;  some  Garnets 
show  asterism.  Most  Garnets  fuse  more  or  less  easily,  but 
Uvarovite  is  almost  infusible.  The  specific  gravity  varies 
from  3'15  to  4*3  in  the  various  kinds.  The  fracture  is 
conchoidal  to  subconchoidal  or  uneven,  and  most  speci- 
mens are  brittle.  The  hardness  is  from  6J  to  7J.  An 
indistinct  cleavage  parallel  to  the  faces  of  the  dodecahedron 
is  sometimes  present ;  the  streak  is  white. 


FIG.  23.— Garnet.  FIG.  24.— Garnet. 

The  crystalline  form  is  in  all  Garnets  cubic,  and  the 
commonest  forms  are  the  dodecahedron  (Fig.  23),  and  tris- 
octahedron  (Fig.  24).  The  crystals,  when  in  situ,  are  more 
often  found  embedded  in  a  matrix,  and  they  are  then  usually 
idiomorphic ;  less  often  they  are  found  attached  at  one 
point  to  the  wall  of  a  cavity.  Garnets  are  usually  of 
secondary  origin,  developed  sometimes  in  metamorphosed 
calcareous  rocks,  more  often  in  eruptive  rocks  (Figs.  25 
and  26). 

In  chemical  composition  the  Garnets  are  orthosilicates 
of  the  form  3  K"0,  K'g'  03,  3  Si02,  where  K"  may  represent 


STONES.  245 

calcium,  iron,  magnesium,  or  less  frequently  manganese  or 
chromium,  and  R"'  represents  aluminium,  iron,  or  chromium. 
The  Garnets  are  thus  grouped — 
Aluminium  Garnet  I.     A.  Aluminium-Calcium    Garnet — 

Hessonite*. 
B.  Aluminium-Magnesium    Garnet 

— Pyrope. 
c.  Aluminium -Iron       Garnet— 

Almandine. 
D.  Aluminium-Manganese     Garnet 

— Spessartite. 
Iron      Garnet     II.     E.  Calcium-Iron      Garnet — Andra- 

dite. 
Chromium  Garnet  III.    F.  Calcium-Chromium     Garnet — 

Uvarovite. 

Those  Garnets  which  are  rich  in  iron  fuse  more  easily, 
and  some  of  them  show  magnetic  properties ;  most  garnets 
resist  all  acids  except  hydrofluoric.  Heat  in  most  cases 
causes  an  alteration  in  colour,  but  the  colour  is  usually 
restored  on  cooling.  The  colour  depends  on  the  chemical 
composition,  and  thus  is  uniformly  distributed. 

HESSONITE  is  also  known  as  Essonite,  Grossular,  or  Cinna- 
mon-stone. The  colour  is  usually  some  shade  of  reddish 
brown,  but  may  be  yellow-brown,  honey  yellow,  pale  green, 
or  pale  red ;  some  specimens  look  more  red  at  a  distance 
and  more  yellow  when  close  to  the  eye.  The  specific  gravity 
is  3*44  to  3 '62,  and  the  hardness  is  7J. 

Ceylon  is  the  most  important  locality ;  in  the  extreme 
south  of  the  island  at  Belligam  it  is  found  in  a  gneiss,  while 
at  Matura  it  occurs  in  the  gravels.  Most  of  the  Hessonite 
used  as  a  gem  comes  from  this  part. 


246 


PKECIOUS  STONES. 


In  the  Alps  it  is  found  in  serpentine  at  the  Mussa  Alp 
in  Piedmont  with  Alalite  and  Chlorite ;  this  variety  is 
sometimes  spoken  of  as  Succinite  on  account  of  its  amber- 
colour.  A  group  of  crystals  is  shown  in  Fig.  27.  In  the 
Maigels-Thal  it  occurs  in  mica-schist  with  Epidote.  It  is 
also  found  in  the  Ural  Mountains  and  elsewhere. 

A   variety   of   Hessonite,   known   more   particularly   as 


FIG.  25. — Garnet  Crystals  in  the  Matrix. 

Grossular,  of  a  greenish  colour,  is  sometimes  used  as  a 
gem,  when  it  is  called  Gooseberry  Stone ;  it  is  found  in 
Siberia.  A  pale  red  variety  from  Mexico  has  also  been  cut; 
it  is  found  in  transparent  crystals  in  a  limestone. 

PYROPE,  often  called  the  Bohemian  Garnet  from  its 
important  occurrence  in  Bohemia,  includes  some  Precious 
Garnet  and  Vermeille  (see  Almandine) ;  sometimes  it  is 
known  as  Kock  Euby.  The  colour  ranges  from  blood-red 
to  hyacinth-red  and  yellow  in  one  direction,  and  to  black 


PRECIOUS  STONES. 


247 


in  the  other.  It  practically  always  occurs  in  transparent 
fragments,  each  fragment,  however,  being  free  from  flaws 
and  of  a  very  uniform  quality.  It  is  always  derived  from 
basic  rocks.  The  specific  gravity  is  3'70  to  3*78 ;  the  hard- 
ness is  7J.  The  refractive  index  for  red  light  is  T79,  it 
never  shows  anomalous  refraction,  and  it  is  very  infusible. 


FIG.  26.— A  Group  of  Garnet  Crystals. 

The  colour  depends  on  the  presence  of  iron  and  manganese, 
and  perhaps  chromium  also.  It  is  found  in  Bohemia  in 
a  decomposed  basic  rock  and  in  detritus  from  this  near 
Meronitz,  Podsedlitz,  and  Budweis ;  in  Saxony,  at  Zoblitz; 
in  Scotland,  at  Elie  in  agglomerate ;  and  in  South  Africa 
in  the  Diamond  bearing  agglomerates  where  both  a  paler 
red  and  blood-red  colours  (Cape  Ruby)  occur,  associated 


248 


PKECIOUS  STONES. 


with  the  minerals  mentioned  under  "  Diamond."  In 
the  United  States  it  is  found  in  Arizona  (Arizona  Ruby), 
in  Colorado  (Colorado  Ruby)  and  in  New  Mexico.  It  also 
occurs  in  Mexico. 

ALMANDINE,  which  is  known  under  the  various  names 
Precious  Garnet,   Common  Garnet,  and  Oriental  Garnet, 


FiG.27.—  Garnet  with  Alalite. 

was  the  Carbunculus  Alabandicus  of  Pliny,  being 'named 
after  Alabanda  in  Caria,  which,  if  not  a  locality  where  it 
occurs,  was  at  any  rate  an  important  trading  centre  for.  it. 
The  colour  is  red  of  a  deep  shade  in  the  gem  variety,  some- 
times inclining  to  a  columbine  red ;  the  brownish  red 
shades  are  used  under  the  name  of  Vermeille  (see  Pyrope), 
but  this  kind  is  less  valued.  It  often  occurs  transparent. 


fBECtOUS   STONES.  249 

Its  specific  gravity  is  3'95  to  4*29,  its  hardness  is  7J,  its 
index  of  refraction  for  red  light  is  1*77,  and  it  has  the 
peculiarity  of  showing  absorption  bands  in  the  spectrum. 
It  fuses  easily  before  the  blowpipe,  and  is  slightly  magnetic. 

It  is  a  widely  distributed  form  of  Garnet ;  the  principal 
localities  for  the  gem  qualities  are  in  the  East.  In  Ceylon 
it  is  found  in  fine  crystals  in  mica-schist  near  Trincomali ; 
it  also  occurs  in  the  gravels  ;  from  this  occurrence  it  is 
sometimes  known  as  Ceylonese  Euby.  The  so-called 
"Syrian"  Garnet  was  supposed  to  come  from  Suriam  in 
Pegu  (Lower  Burma),  but  its  occurrence  is  not  authenticated 
here.  The  term  refers  now  rather  to  Garnet  of  a  violet 
shade  than  to  material  from  any  special  place. 

In  India  it  is  found  at  the  Sarwar  mines  in  Rajputana, 
near  the  Godivari  river  in  gneiss,  in  Haiderabad,  and  at 
Kakoria  in  Jaipur. 

In  Brazil  it  is  found  in  the  Minas  Novas  district ;  in 
Australia  a  kind  known  as  Adelaide  Euby  is  found  in  the 
north  of  South  Australia ;  in  the  United  States  on  the 
Columbia  Biver;  and  in  Europe  in  the  Ziller  Thai  in  the 
Tyrol,  in  schist. 

SPESSARTITE  is  of  a  dark  hyacinth-red  colour  with  a  specific 
gravity  of  4'0  to  4'3.  Transparent  material  suitable  for 
gem  use  has  been  found  at  the  Mica  mine  near  Amelia 
Court  House  in  Virginia,  United  States. 

ANDRADITE,  called  also  Common  Garnet  and  Black  Garnet, 
includes  three  varieties  sometimes  used  as  precious  stones. 
In  general  Andradite  occurs  in  many  shades  of  yellow, 
green,  brown  and  grey ;  some  in  black.  The  specific 
gravity  is  3'83  to  3'90. 

The  variety  Demantoid   is  found   of   a   grass-green   to 


250  PBECIOTJS  STONES. 

emerald  -  green  colour,  or  sometimes  colourless.  The 
emerald-green  form  contains  chromium.  It  has  a  high 
lustre,  almost  adamantine;  the  refractive  index  is  greater 
than  in  most  Garnets,  and  the  dispersion  much  more 
marked,  hence  there  is  some  play  of  colour  in  a  cut  speci- 
men. It  occurs  in  transparent  masses,  rarely  in  crystals. 
It  is  softer  than  the  other  Garnets,  being  only  equal  to 
6|-.  The  mineral  is  more  easily  attacked  by  acids  than 
other  membsrs  of  the  group,  but  it  is  very  infusible.  It 
is  found  in  the  Ural  Mountains  (and  so  is  sometimes  called 
Uralian  Emerald)  at  Nizhni  Tagilsk  in  gold  washings,  and 
in  situ  in  serpentine  in  the  Sissersk  district. 

Topazolite,  another  variety  of  Andradite,  is  found  at  Ala 
in  Piedmont ;  in  colour  it  is  a  yellow  inclining  to  green. 

Melanite,  a  common  black  form  of  Andradite  (Fig.  25), 
occurs  at  Frascati  near  Kome  and  in  Baden.  It  is  used 
sometimes  in  mourning  jewellery. 

UVAROVITE,  a  Garnet  of  brilliant  emerald-green  colour 
'containing  chromium,  is  found  in  the  Urals  in  cavities  in 
Chromic  Iron  ;  unfortunately  the  specimens  are  too  small 
to  use  as  gems. 

Rhodolite,  so  called  from  the  similarity  of  its  colour  to 
that  of  the  rhododendron — a  light  red — is  a  Garnet  found 
at  the  Corvee  Creek  Corundum  mines  in  Macon  County  in 
North  Carolina,  United  States.  It  has  a  very  high  lustre 
and  a  freedom  from  flaws  which  makes  it  very  valuable  as 
a  gem.  In  composition  it  is  intermediate  between  Pyrope 
and  Almandine. 

Garnet  is  largely  used  as  an  abrasive,  often  being  made 
into  garnet-paper  similar  to  glass-  and  sand-paper.  Many 
of  the  pivot  bearings  of  good  watches  are  made  of  Garnet 


PEECIOUS  STONES.  251 

also.  It  was  to  some  extent  used  by  the  Greeks  as  a 
material  for  engraving  on,  much  more  so  by  the  Komans. 
Barbot,  in  his  inventory  of  the  French  jewels,  made  in  1791, 
mentions  two  cups  made  of  Garnet  of  three  inches  in  height, 
and  several  smaller  ones.  It  is  usually  cut  en  cabochon, 
often  in  a  meniscoid  form  so  as  to  thin  the  material  when 
the  colour  is  too  deep;  such  thin  stones  are  often  known  as 
"  Garnet  Shells."  Paler  coloured  stones  are  either  mixed 
cut,  step  cut,  or  table  cut.  Pyrope  is  often  cut  with  a 
convex  upper  surface  facetted  near  the  girdle,  and  step  cut 
below  ;  sometimes  it  is  cut  as  a  brilliant  or  a  rose.  Large 
specimens  of  Pyrope  are  very  rare.  Hessonite  is  usually 
cut  with  facets  and  mounted  with  foil  in  a  closed  setting  ;  it 
is  rarely  cut  en  cabochon ;  sometimes  it  is  sold  as  Hyacinth, 
more  especially  in  the  case  of  the  deeper  coloured  varieties; 
it  appears  more  brilliant  in  artificial  light.  The  lighter 
varieties  of  Garnet  are  sometimes  mounted  in  an  open  set- 
ting. The  most  valuable  kinds  are  the  finely  coloured 
Almandine,  a  good  specimen  of  which  approaches  the  Sap- 
phire in  value,  and  the  Pyrope,  which  in  moderate  sized 
specimens  may  be  worth  £10  per  carat. 

Most  minerals  with  which  Garnet  may  be  confused  are 
doubly  refracting,  thus  Zircon,  Corundum,  Olivine,  and 
Beryl  are  all  distinguished  by  this  property.  Spinel,  how- 
ever, is  singly  refracting  like  Garnet,  and  is  very  near  it  in 
hardness  and  specific  gravity  and  often  in  colour.  The 
crystals  are  of  a  different  habit,  Spinel  being  usually 
octahedral,  but  this  is  of  no  help  in  a  cut  specimen,  nor  is 
chemical  analysis.  Kuby  is  lighter  than  Almandine  and 
heavier  than  Pyrope,  thus  Almandine  is  also  denser  than 
Pyrope.  Euby  may  be  distinguished  from  any  Garnet  by 


252  PKECIOUS  STONES. 

its  dichroism ;  it  is  harder  too.  Olivine  (Chrysolite)  and  Beryl 
(Emerald)  are  both  lighter  than  Demantoid  and  are  both 
doubly  refracting,  though  Olivine  is  only  feebly  dichroic. 
Zircon  (Hyacinth)  is  denser  and  harder  than  Hessonite 
and  has  a  much  higher  lustre.  Glass  imitations  in  all 
cases  are  softer. 


CHAPTEE  XIII. 


376.    OLIVTNE SPHENE. 

SOME  of  the  minerals  known, to  the  ancients  as  Beryllus, 
Smaragdus,  and  Topazios  may  have  been  Olivine ;  but 
their  Chrysolithus  was  our  Topaz,  although  Olivine  is  now 
known  sometimes  as  Chrysolite.  When  undecomposed, 
Olivine  is  some  shade  of  green,  usually  olive-green  or 
greyish-green,  but  on  exposure  to  weathering  it  turns 
brown  or  red  through  the  formation  of  ferric  salts.  It  is 
transparent  in  the  gem  varieties,  and  has  a  vitreous  lustre. 
It  shows  strong  double  refraction,  the  refractive 
indices  in  yellow  light  being,  for  the  greatest 
T697,  and  for  the  least  1*661.  Dispersion  is 
weak,  and  it  is  only  feebly  dichroic.  When 
heated  it  turns  white,  but  does  not  fuse  easily. 
The  specific  gravity  is  3'33  to  3'44.  The 
fracture  is  conchoidal,  and  the  mineral  is  brittle. 
It  has  two  cleavages,  neither  very  perfect, 
normal  to  the  two  horizontal  axes  of  the  crystal. 
The  hardness  is  6J  to  7 ;  the  streak  is  usually 
white.  It  is  orthorhombic  in  crystalline  form,  and  commonly 
occurs  in  stout  rhombic  prisms  (Fig.  28) .  Sometimes  twinned 
forms  are  seen ;  more  often  it  occurs  as  embedded  grains, 
thus  often  allotriomorphic.  It  is  practically  always  found, 
when  in  situ,  in  basic  eruptive  rocks  as  an  original 


\ 


FIG.  28. 
Olivine. 


254  PEECIOUS  STONES. 

constituent.  In  composition  it  is  an  orthosilicate  of 
magnesium  and  iron,  2  (MgFe)O,  Si02.  Olivine  is  easily 
decomposed  by  the  mineral  acids,  and,  according  to  Max 
Bauer,  this  is  the  rationale  of  the  mixing  of  sulphuric  acid 
with  the  final  polishing  material  instead  of  water. 

Olivine  of  a  pure  olive-green  colour,  and  transparent, 
suitable  for  gem  cutting,  is  known  as  Noble  Chrysolite  or 
Peridot.  Although  Olivine  is  found  in  such  abundance, 
most  of  it  as  it  occurs  in  eruptive  rocks  is  in  such  small 
grains,  or  so  cloudy  or  fractured,  as  to  be  unsuitable  for  use  ; 
and  it.  is  a  remarkable  fact  that  there  is  hardly  a  locality- 
known  where  Noble  Chrysolite  is  now  to  be  found,  even  in 
gravel  deposits.  Dr.  Kunz  is  of  the  opinion  that  most 
now  seen  uncut,  or  roughly  cut,  is  material  derived  from 
long  lost  deposits,  and  the  only  definite  localities  now  known 
are  in  the  United  States,  in  Arizona,  and  New  Mexico,  and 
there  gem  material  is  very  scarce.  Of  the  stones  for 
which  Chrysolite  may  be  mistaken  Emerald,  Prehnite,  and 
Tourmaline  are  less  dense ;  Topaz  is  of  the  same  density, 
but  harder,  and  Chrysoberyl  and  Corundum  are  denser  ; 
further,  Emerald,  Chrysoberyl,  Corundum,  and  Tourmaline 
are  harder.  Glass  imitations,  and  the  so-called  Bottle  Stone, 
are  singly  refracting.  Olivine  is  usually  either  step  cut  or 
mixed  cut ;  as  a  pendant  stone  it  may  be  cut  as  a  double 
rosette.  Its  value  is  about  equal  to  that  of  Topaz. 

382.  PHENAKITE. 

Phenakite  is  a  mineral  that  only  occurs  sparingly  in 
Nature,  and  it  is  not  very  much  used  as  a  gem.  It  is  found 
colourless,  wine  yellow,  rose  pink,  and  brown.  The  speci- 
mens used  as  gems  are  always  transparent.  It  is  doubly 


PKECIOUS   STONES.  255 

refractive,  the  indices  for  yellow  light  being  1*654  and  1*670. 
The  dispersion  is  weak,  and  hence  there  is  but  little  fire  in 
the  stone  when  cut.  The  lustre  is  vitreous,  and  the  mineral 
is  capable  of  taking  a  high  degree  of  polish.  The  specific 
gravity  is  2*95  to  3*00.  It  has  a  conchoidal  fracture,  and 
is  brittle.  There  is  a  perfect  cleavage  parallel  to  the  prism 
face,  and  an  imperfect  one  parallel  to  the  primary  rhombo- 
hedron.  It  crystallises  in  rhombohedral  forms,  and  the 
habit  is  either  stoutly  prismatic  or  rhombohedral.  In 
composition  it  is  a  beryllium  orthosilicate,  Be2  Si04.  It  is 
found  in  mica-schist  with  Emerald  and  Chrysoberyl,  at 
Takovaya,  in  the  Ural  Mountains;  also  on  the  Ilmen 
Mountains  with  Amazonstone  and  Topaz.  In  America  it 
is  found  16  miles  from  Pike's  Peak,  in  Colorado ;  at  Topaz 
Butte,  with  Topaz  and  Amazonstone  in  granite ;  also  at 
Mount  Antero,  in  Colorado,  with  Quartz  and  Beryl.  The 
chief  demand  for  the  gem  is  in  the  countries  where  it  is 
mostly  found — Russia  and  America.  The  colourless 
specimens  are  cut  as  brilliants,  and  mounted  in  an  open 
setting,  and  the  coloured  ones  may  be  treated  in  the  same 
way  if  the  shade  is  good. 

383.  DIOPTASE. 

Dioptase  and  Malachite  are  of  interest  among  gem  stones 
on  account  of  the  large  percentage  of  the  common  metal 
copper  entering  into  their  composition.  One  might  almost 
call  Dioptase  a  copper  ore,  and  certainly  Malachite  is.  In 
colour  it  is  emerald-green,  but  of  a  deeper  tint  than  the 
Emerald  itself  has ;  the  lustre  is  vitreous ;  it  is  transparent 
to  translucent  and  shows  strong  double  refraction,  the 
indices  being  1*667  and  1*723.  When  heated  it  turns 


256 


PEECIOUS  STONES. 


black,  and  water  is  given  off.  The  specific  gravity  is  3*27 
to  3'35,  it  has  a  conchoidal  fracture  and  is  brittle.  The 
hardness  is  only  equal  to  5  of  Mohs'  scale  ;  there  is  a  perfect 
rhombohedral  cleavage.  The  streak  is  green.  Its  crys- 
talline form  is  rhombohedral  and  it  usually  occurs  as  stout 
prisms  (Fig.  29).  The  crystals  are  small.  It  is  formed  by 
the  decomposition  of  copper  ores,  and  hence  usually  is 
associated  with  other  copper  compounds.  In  composition 
it  is  a  basic  silicate  of  copper,  H20  CuO  Si02.  It  is 
found  in  druses  in  a  limestone  at  the  hill 
of  Altyn-Tiibe  on  the  Altai  Mountains,  also 
on  the  Malaya  Eiver  in  Trans-Baikal ;  also 
in  Hungary  and  Chile.  Good  crystals  have 
more  recently  been  obtained  at  Mindouli, 
east  of  Comba,  in  the  French  Congo,  asso- 
ciated with  Chrysocolla.  Dioptase  is  not 
extensively  used  as  a  gem,  largely  on 
account  of  the  difficulty  of  obtaining  good 
specimens,  but  also  because  of  its  liability 
to  damage ;  in  colour  it  is  undoubtedly  very 
fine.  It  is  readily  distinguished  from  Emerald  by  the 
deeper  colour,  higher  specific  gravity  and  inferior  hardness. 

393.  IDOCEASE. 

This  mineral,  which  is  also  known  as  Vesuvian  on 
account  of  its  occurrence  on  Vesuvius,  is  not  extensively 
used  as  a  gem.  The  colour  is  usually  brown,  sometimes  a 
clear  green,  and  more  rarely  bright  yellow  or  pale  blue. 
The  gem  varieties  are  transparent,  and  the  lustre  is  vitreous. 
The  mineral  is  doubly  refracting,  both  the  ordinary  and 
extraordinary  rays  being  a  good  deal  deflected,  but  in  a 


FIG.  29. 
Dioptase. 


PEECIOUS  STONES. 


257 


nearly  equal  degree.  The  indices  of  a  green  crystal  for 
yellow  light  were  found  to  be  1*719  and  1-718.  Dichroism 
is  well  marked,  a  green  crystal  showing  images  in  the 
dichroscope  respectively  a  pure  green  and  a  yellow-green. 
It  fuses  before  the  blowpipe.  The  specific  gravity  is  3'35 
to  3-45.  The  fracture  is  subconchoidal,  and  the  mineral  is 
brittle.  The  hardness  is  6£,  and  the  streak  white.  The 
crystalline  form  is  tetragonal  and  the  crystals  are  usually 
short  prisms,  terminated  by  a  pyramid  and  the  basal  face 
(Fig.  30).  The  crystals  are  often 
highly  modified.  Two  cleavages  are 
present,  one  a  prismatic  one  and  the 
other  parallel  to  the  basal  plane. 
Idocrase  is  always  found  in  calcareous 
rocks  which  have  undergone  thermo- 
metamorphism  (Fig.  31).  In  chemical 
composition  it  is  a  basic  calcium 
aluminium  silicate,  but  the  exact 
formula  is  not  very  certain,  possibly 
2  H20,  12  CaO,  3  (AlFe)203,  10  Si02.  Iron,  manganese 
and  magnesium  are  sometimes  present,  and  the  two 
first  elements  may  considerably  modify  the  colour.  It  is 
a  mineral  of  wide  distribution,  but  many  forms  are 
opaque  or  only  subtranslucent,  and  the  only  localities  from 
which  material  has  been  obtained  for  gem  use  are  in  Italy, 
with  the  exception  of  the  variety  Xanthite,  a  brown  Idocrase 
found  near  Amity  in  New  York  State.  In  Italy  the  brown 
crystals  are  found  in  the  ejected  blocks  of  Monte  Somma, 
of  which  volcano  Vesuvius  is  a  later  cone ;  at  this 
locality  the  mineral  is  associated  with  a  great  number  of 
interesting  species.  It  also  occurs  in  Piedmont,  on  the 
P.S.  s 


FIG.  30.— Idocrase. 


258 


PRECIOUS  STONES. 


Mussa  Alp  in  the  Ala  Valley,  the  exact  spot  being 
called  Testa  Ciarva,  a  locality  already  mentioned  in  con- 
nection with  Hessonite  and  Diopside.  When  used  as  a 
gem,  Idocrase  is  either  step  cut  or  table  cut.  There  are 
several  minerals  with  which  Idocrase  may  be  confounded  ; 
of  these  Zircon  and  Demantoid  Garnet  are  distinctly 
heavier,  both  are  harder,  and  Garnet  is  singly  refracting. 


PIG.  31. — Idocrase  in  the  Matrix. 

Quartz  (Cairngorm),  Tourmaline  and  Diopside  are  lighter, 
Quartz  and  Tourmaline  being  harder  and  Diopside  softer 
than  Idocrase.  Axinite  is  slightly  less  dense,  slightly 
harder,  and,  more  important,  it  shows  violet,  brown  and 
green  colours  in  different  directions.  Olivine  is  rather 
more  yellow  in  colour,  and  is  very  feebly  dichroic.  Epi- 
dote  is  slightly  denser  than  Idocrase,  slightly  softer  and 
strongly  pleochroic,  showing  green,  yellow,  and  brown  tints 
in  different  directions. 


PEECIOUS  STONES. 


259 


394.  ZIECON. 

There  has  been  much  confusion  about  the  relation  to 
this  species  of  some  of  the  minerals  spoken  of  by  Pliny,  but 
it  seems  well  established  that  theLyncurium  of  Theophrastus 
was  our  Zircon  in  part.  It  is  supposed  it  was  the  seventh 
stone,  the  Ligure,  of  the  Rationale  of  the  High  Priest. 
Zircon  is  usually  found  in  some  shade  of  brown,  ranging 
from  a  pale  yellowish-brown  to  a  rich  red-brown;  only 


FIG.  32.— Zircon : 
Typical  Form. 


FIG.  33.— Zircon : 

Unequally  developed 

Crystal. 


rarely  is  it  colourless,  green  or  violet.  It  varies  from 
transparent  to  opaque,  those  varieties  used  as  a  gem  being 
transparent  or  subtransparent.  The  lustre  is  distinctly 
adamantine.  The  mineral  is  doubly  refracting  in  a  marked 
degree,  and  the  actual  deviation  is  greater  than  in  any  other 
gem  stone  except  the  Diamond,  the  values  of  the  indices 
for  yellow  light  being  T923  and  1^968.  The  dispersion, 
however,  is  feeble,  so  that  the  mineral  when  cut  shows  a 
lack  of  fire ;  the  dichroism  is  very  feeble ;  there  is  a  marked 
phosphorescence  on  heating.  Zircon  is  peculiar  in  showing 

s  2 


260  PBEdOUS  STONES. 

absorption  bands  in  the  spectrum,  as  was  indicated  by  Pro- 
fessor Church.  The  specific  gravity  is  very  variable, 
usually  4*6  to  4*7,  but  it  may  range  from  4'2  to  4'86.  The 
fracture  is  conchoidal,  the  mineral  is  brittle,  and  there  are 
two  cleavages,  one  prismatic  and  the  other  parallel  to  the 
faces  of  a  pyramid,  but  neither  are  distinct.  The  hardness 


FIG.  34. — Zircon,  in  a  Pegmatite  Matrix. 

is  7J ;  the  streak  is  uncoloured.  Zircon  crystallises  in  the 
tetragonal  system,  and  is  usually  found  in  rather  elongated 
forms,  as  shown  in  Fig.  32.  Some  crystals  are  unequally 
developed  and  complex  (Fig.  33) ;  more*  rarely  the  prism 
faces  are  poorly  developed  or  absent.  Twinned  forms  occur? 
the  component  parts  meeting  one  another  in  a  form  likened 
to  the  bent  knee.  Zircon  is  found  as  a  secondary  mineral 


PEECIOUS  STONES.  261 

chiefly  in  eruptive  rocks  that  have  undergone  alteration, 
especially  alteration  by  deformation.  Crystals  of  Zircon 
in  a  pegmatite  matrix  are  shown  in  Fig.  34.  In  composi- 
tion it  is  a  silicate  of  zirconium,  ZrSi04-  Some  interesting 
changes  are  seen  on  heating  the  mineral ;  thus  a  deep  red- 
brown  specimen  heated  in  the  dark  will  be  seen  to  phos- 
phoresce suddenly,  and  it  will  then  be  found  that  the  stone 
is  changed  to  a  very  pale  yellow  colour,  or  has  become 
colourless  altogether ;  the  specific  gravity  is  increased,  and 
the  lustre  is  rendered  greater.  Some  of  these  changes  are 
supposed  to  be  due  to  chemical  alterations  in  the  state  of 
the  iron  contained  in  almost  all  specimens  of  the  mineral. 
Even  strong  light  may  cause  the  stone  to  change,  but  the 
colour  is  to  some  extent  restored  by  keeping  the  specimen 
in  the  dark  for  a  time  afterwards.  With  the  ordinary 
variety  of  Zircon  we  are  not  much  concerned.  The  gem 
variety  occurs  as  Hyacinth,  which  includes  the  orange  and 
red-brown  transparent  stones,  and  Jargon,  comprising  the 
colourless  and  pale  yellow  specimens. 

Most  of  the  stones  suitable  for  use  as  gems  are  found  in 
the  gem  gravels  of  Ceylon,  which  gravels  are  derived  from 
the  weathered  crystalline  rocks  in  which  the  Sapphires 
were  developed.  The  chief  localities  are  Eatua-pura  and 
Matura,  the  latter  locality  giving  its  name  to  the  "  Matura 
Diamonds,"  which  ar,e  very  pale  or  colourless  Zircons. 
Many  other  localities  yield  the  mineral,  but  rarely  in  gem 
quality.  Such  are :  Bohemia,  where  it  occurs  in  gneiss ; 
near  Unask,  in  the  Ural  Mountains ;  at  Friedriksvarn  in 
Norway  in  the  zircon-syenite ;  at  Mudgee  in  New  South 
Wales  in  the  auriferous  alluvium  ;  and  in  the  volcanic 
districts  of  France, 


262  PEECIOUS  STONES. 

Zircon,  besides  its  use  as  a  gem,  is  now  of  great  value  as 
a  source  of  the  oxide  Zirconia ;  and  in  North  Carolina,  in 
the  United  States,  it  is  extensively  mined,  as  well  as  in 
other  parts. 

Use  is  made  of  the  effect  of  heat  in  discharging  the 
colour  of  dark  Zircon  to  produce  colourless  specimens,  and 
such  have  been  substituted  for  Diamond,  which  they  much 
resemble,  on  account  of  their  adamantine  lustre,  though 
they  lack  the  fire  of  the  Diamond.  The  great  density  of 
Zircon  is  of  much  help  in  its  identification.  The  Garnets 
are  distinguished  by  their  single  refraction,  and  so  is 
Diamond,  the  latter  also  showing  more  "  fire."  Of  the 
doubly  refracting  minerals,  Corundum  is  the  only  one  likely 
to  be  confused  with  Zircon  that  approaches  it  in  density, 
and  the  Oriental  Hyacinth,  as  it  is  called,  is  strongly 
dichroic. 

397.  TOPAZ. 

What  we  know  now  as  Topaz  was  not  the  Topazius  of 
Pliny,  which  seems  rather  to  have  been  our  Olivine ;  it  may 
have  been  included  in  part  in  Pliny's  term  Chrysolithus. 

Topaz  occurs  colourless  and  more  frequently  of  a  straw 
or  amber  colour,  or  pale  green  or  blue ;  more  rarely  pink. 

The  lustre  is  vitreous  and  especially  bright  on  the  prism 
faces ;  the  cleavage  plane  shows  a  pearly  lustre.  The 
mineral  in  the  kinds  used  as  gems  is  transparent,  though 
less  clear  forms  are  also  found.  It  is  doubly  refracting,  but 
the  indices  of  refraction  do  not  differ  greatly  from  one 
another,  and  they  are  not  of  high  value  ;  nor  is  there  much 
difference  in  the  indices  for  differently  coloured  rays.  Thus 
the  greatest  and  least  values  for  the  B  line  in  the  red  part 


PBECIOUS  STONES.  263 

of  the  spectrum  are :  for  a  crystal  from  Siberia,  1*619  and 
1'610,  while  for  the  F  line  in  the  blue  portion  of  the 
spectrum  they  are  T628  and  1'619.  Thus  there  is  but 
little  "fire"  in  a  cut  specimen  of  Topaz,  but  coloured 
varieties  show  distinct  dichroism.  Before  the  blowpipe  it 
is  infusible,  but  the  effects  of  heat  are  nevertheless  impor- 
tant in  the  case  of  Topaz.  In  1755  a  French  jeweller 
named  Dumelle  found  that  on  gradually  heating  a  yellow 


FIG.  35. — Blue  Topaz  with  Smoky  Quartz. 

Topaz  the  colour  changed  to  a  pink,  and  this  effect  has 
been  made  use  of  in  the  artificial  production  of  a  pink 
colour,  a  process  now  known  as  "  pinking  "  or  "  burning," 
and  one  by  which  most  of  the  pink  stones  now  sold  are 
produced.  To  effect  this  change  the  mineral  must  be 
heated  and  cooled  again  very  gradually  to  avoid  producing 
flaws ;  it  may  be  heated  in  a  sand  bath,  or  packed  with 
charcoal  in  a  small  crucible,  or  embedded  in  clay  and  then 
baked,  or,  finally,  it  may  be  wrappec^  in  several  layers  of 


264 


PRECIOUS  STONES. 


amadou  or  German  tinder,  the  whole  bound  with  wire  and 
the  tinder  lighted  and  allowed  to  smoulder  away ;  if  the 
heating  is  too  great  the  stone  will  be  completely  decolorised. 
It  is  remarkable  that  a  "burnt"  Topaz  shows  more  marked 
dichroism  than  the  unaltered  mineral,  images  of  a  cherry 


PIG.  36.— Topaz. 

red  and  a  pale  yellow  being  seen  in  the  dichroscope.  The 
fact  that  Topaz  may  be  so  strongly  heated  without  destroy- 
ing the  colour  points  to  the  colour  not  being  due  to  organic 
matter;  but  in  some  Topaz  organic  matter  does  seem  to 
account  for  the  colour.  Certain  specimens  of  yellow  and 
blue  Topaz  are  found  to  change  their  tints  on  exposure 
to  strong  light,  for  instance.  Topaz  becomes  strongly 


PEECIOUS  STONES. 


265 


electrified  when  rubbed,  or  in  some  cases  when  pressed, 
and  on  heating. 

The  specific  gravity  of  Topaz  lies  between  3'40  and  3*65. 
The  fracture  is  subconchoidal ;  the  mineral  has  a  hardness 
of  8  of  Mohs'  scale,  and  is  brittle.  The  streak  is  colourless. 
There  is  a  highly  perfect  cleavage  normal  to  the  vertical 
axis  of  the  crystal.  The  crystalline  form  is  orthorhombic 
and  the  habit  prismatic  (Fig.  35),  the  prism  usually  show- 
ing the  faces  of  two  forms  at  least,  and  often  being  verti- 
cally striated,  as  is  well  shown  in  Fig.  36.  Crystals  often 
show  an  apparent  want  of  symmetry 
(Fig.  37).  Topaz  is  usually  found,  when 
in  situ,  in  attached  crystals  in  cavities 
in  granite,  in  some  dynamo-metamor- 
phosed rocks  (which  have  probably 
been  acted  on  by  thermo-metamorphiftm 
as  well),  and  in  some  acid  lavas  known 
as  liparites,  though  the  last  occurrence 
seems  rare.  It  will  be  seen  that  Topaz  -pIG  3~  _Topaz . 
is  thus  more  often  found  in  rocks  rich  unequally  developed 
in  Quartz.  It  is  also  associated  fre-  Crystal. 

quently  with  Beryl,  Tourmaline,  and  Felspar,  especially 
where  these  have  separated  from  a  granite  magma  in  the 
later  stages  of  consolidation.  Other  frequent  associates  are 
Apatite,  Fluor  Spar,  Cassiterite,  and  Mica.  Topaz  is 
resistent  to  most  forms  of  weathering  and  hence  is  often 
found  in  rolled  pebbles  in  the  detritus  from  such  rocks  as 
have  been  mentioned.  In  composition  it  is  a  fluo-silicate 
of  aluminium,  [Al(0,  F2)]  AlSi04.  Water  is  usually  present 
in  small  quantity  as  an  essential  constituent,  probably  with 
the  hydroxyl  group  (OH)  replacing  some  of  the  fluorine. 


266  PBECIOUS  STONES. 

Topaz  is  of  very  wide  distribution ;  in  England  it  is 
found  with  Cassiterite  at  St.  Michael's  Mount ;  in  Scotland 
water-worn  crystals  of  the  pale  blue  (eau  de  nil)  colour  are 
found  in  gravels  in  Aberdeenshire  ;  and  bright  though 
small  crystals  occur  in  the  Mourne  Mountain  granite  in 
Ireland.  Some  of  the  Scottish  specimens  have  been  cut 
into  very  beautiful  stones,  but  these  British  occurrences  are 
insignificant  when  compared  to  some  of  the  foreign  ones. 
In  the  Ural  Mountains  near  Musinka  blue  crystals  are 
found :  these  are  sometimes  known  as  Siberian  or  Tauridan 
Topaz.  Colourless  specimens  are  found  near  Miask  in  the 
Ilmen  Mountains  ;  while  in  the  district  of  Nerchinsk,  in 
the  Adun-Chalon  Mountains,  very  fine  blue-green  Topaz 
occurs  ;  and  on  the  Urulga  River  blue  and  yellow  crystals 
are  found,  some  of  them  of  large  size,  one  in  the  Russian 
Imperial  collection  weighing  22J  Ibs.  The  Urulga  speci- 
mens are  very  prone  to  change  colour  on  exposure  to  a 
strong  light.  Topaz  of  various  colours  has  been  found  in 
Kamshatka. 

Brazil  is  perhaps  the  most  important  locality.  Here,  in 
the  State  of  Minas  Geraes,  in  the  north-east,  the  gravels 
near  Novas  Minas  afford  colourless  and  variously  coloured 
specimens ;  of  these  the  richer  blue  ones  are  known  as 
Brazilian  Sapphire,  and  the  deeper  red  ones,  which  are  very 
rare,  as  Brazilian  Ruby.  In  the  south-west  of  Minas  Geraes, 
near  Curo  Preto  (Villa  Rica),  various  shades  of  yellow  are 
found  in  a  clay  slate.  The  golden  yellow  crystals  are  known 
as  Brazilian  Topaz  from  their  abundant  occurrence  here. 

In  Ceylon  the  gem  gravels  yield  very  fine  Topaz  in  various 
shades  of  yellow,  and  some  colourless.  The  clear  saffron 
yellow  stones  are  known  as  Indian  Topaz, 


PRECIOUS   STONES.  267 

In  Saxony,  at  Schneckenstein  near  Auerbach,  Topaz  is 
plentifully  found,  clear  yellow  crystals  being  called  Saxon 
Topaz  and  the  greenish  yellow  ones  Saxon  Chrysolite. 

In  the  United  States  yellow  crystals  are  found  in  Con- 
necticut, blue  ones  in  granite  in  Maine,  colourless  ones  in 
Utah,  and  both  colourless  and  pale  blue  occur  with  Amazon- 
stone  at  Florissant  in  the  Pike's  Peak  district  of  Colorado. 
Variously  coloured  Topaz  is  found  with  Cassiterite  in 
Australia  in  Victoria,  while  in  New  South  Wales  colourless 
and  yellow  stones  occur. 

More  recently  blue  Topaz  is  reported  to  have  been  found 
in  Ehodesia. 

Inferior  forms  of  Topaz,  known  as  "  fallow  "  Topaz,  are 
used  as  abrasives. 

Topaz  is  one  of  the  gems  whose  cleavage  may  be  made 
use  of  in  preparing  the  stone  for  cutting,  but  care  has  to  be 
exercised  during  cutting  to  avoid  damage  through  undesired 
cleavage  taking  place,  flaws  or  "  feathers  "  being  very  apt 
to  form  in  this  wray.  Topaz,  when  of  large  size,  is  often 
cut  with  a  large  table  of  generally  elliptical  form,  and  with 
numerous  triangular  facets  between  the  table  and  the 
girdle,  the  lower  part  of  the  stone  being  cut  in  shallow 
steps.  The  ordinary  step  and  table  forms  of  cutting  are 
also  used,  and  for  the  colourless  crystals  (c/outtes  d'eau)  the 
brilliant  cut  may  be  used.  Most  Topaz  is  mounted  in  a 
closed  setting,  often  with  foil  at  the  back.  Topaz  is  not 
worth  nearly  so  much  now  as  it  was  at  one  time,  largely  on 
account  of  change  of  fashion.  A  fine  stone  of  2  carats 
would  now  only  be  worth  about  £1. 

Diamond  and  Spinel  can  be  distinguished  from  Topaz, 
both  being  singly  refracting ;  Diamond  is,  of  course,  much 


268  PRECIOUS   STONES. 

harder ;  coloured  Spinels  are  not  dichroic.  Quartz, 
Phenakite  and  Tourmaline  are  less  dense,  and  Aquamarine 
shows  yellowish  and  sky  blue  images  in  the  dichroscope, 
while  blue  Topaz  shows  colourless  and  green  images. 
Corundum  is  more  dense.  Fluor  Spar  is  very  much  softer 
and  shows  single  refraction.  Topaz  when  yellow  shows 
pale  yellow  and  yellow-red  dichroscope  images ;  burnt 
Topaz  shows  cherry  red  and  honey  yellow.  Further, 
Topaz  is  easily  electrified. 

398.  ANDALUSITE. 

Andalusite,  which  is  also  known  as  Chiastolite,  though 
this  term  is  now  rather  confined  to  a  variety,  is  a  widely 
distributed  mineral,  occurring  as  a  result  of  the  metamor- 
phism  of  argillaceous  rocks  by  hydro- thermal  action.  The 
walls  of  the  old  farm  house  in  Cumberland  in  which  these 
words  are  penned  are  thickly  studded  with  crystals  of  it, 
but  they  are  not  of  gem  quality.  The  only  form  used  as  a 
gem  is  found  in  Brazil  in  the  district  near  Novas  Minas,  in 
gravel.  These  specimens  are  of  green  or  yellow-brown 
colour.  The  mineral  here  is  transparent,  and  has  a  rather 
poor  vitreous  lustre.  It  shows  a  weak  double  refraction, 
the  greatest  and  least  indices  being  1*643  and  1*632.  It, 
however,  shows  a  very  marked  pleochroism  ;  when  viewed 
along  the  vertical  axis  the  colour  is  a  rich  red,  while  in  the 
direction  of  the  horizontal  axes  the  colour  in  both  cases  is 
green,  but  of  slightly  different  tint.  It  is  infusible  before 
the  blowpipe.  Its  specific  gravity  is  3*16  to  3*19.  The 
mineral  is  brittle  and  shows  a  subconchoidal  fracture,  and 
has  a  hardness  of  7j.  There  is  a  distinct  cleavage  parallel 
to  the  face  of  the  rhombic  prism.  The  streak  is  colourless, 


PEECIOUS   STONES.  269 

In  crystalline  form  it  is  orthorhombic,  and  the  habit  is 
usually  prismatic,  though  in  the  variety  Chiastolite  it  is 
more  often  acicular.  In  composition  it  is  a  silicate  of 
aluminium,  A1203  Si02.  The  variety  Chiastolite  shows  a 
cross  when  cut  in  a  plane  normal  to  the  vertical  axis,  and 
when  in  large  crystals  is  sometimes  cut  as  a  charm.  Like 
all  strongly  pleochroic  minerals,  the  colour  effect  must  be 
kept  in  mind  in  cutting.  A  good  specimen  when  cut 
resembles  Alexandrite,  but  is  softer  and  less  dense. 

400.  CYANITE. 

Cyanite,  known  also  as  Sappare  and  Kyanite,  is  closely 
related  to  Andalusite,  both  in  origin  and  composition ;  and, 
like  Andalusite,  thougli  fairly  widely  distributed,  is  but 
rarely  found  in  a  form  suitable  for  gem  use.  It  is  found 
in  various  shades  of  blue,  green,  and  grey.  The  crystals 
often  show  a  good  colour  in  the  centre,  but  are  pale  or 
white  at  the  margins.  The  lustre  is  generally  vitreous,  but 
is  pearly  on  the  cleavage  surfaces  ;  transparent  specimens 
are  rare.  The  double  refraction  is  rather  strong,  the  mean 
index  being  given  as  1'72.  Pleochroism  is  well  marked, 
and  in  the  dichroscope  images  of  two  different  depths  of 
blue  are  seen.  It  is  infusible  ;  the  specific  gravity  is  3'58 
to  3'68.  The  hardness  shows  an  unusual  variation  in  the 
different  directions,  the  least  being  between  4  and  5,  and 
the  greatest  as  much  as  7i-  It  is  a  rather  tough  mineral. 
There  are  two  cleavages,  one  perfect,  the  other  less  so.  In 
crystalline  form  it  is  triclinic,  and  it  usually  occurs  in 
embedded  and  elongated  forms,  with  no  definite  termination ; 
the  crystals  are  often  bent.  Most  of  the  gem  varieties  are 
supposed  to  have  come  from  India,  but  the  exact  locality  is 


270  PKECIOUS   STONES. 

unknown.  It  is  found  in  good  specimens  in  Brazil  near 
Villa  Eica ;  in  the  Alps  on  Monte  Campione  in  the  St. 
Gothard  district  in  schist ;  in  the  Tyrol ;  on  Mount  Greiner 
in  the  Zillerthal ;  and  near  Baskerville,  in  North  Carolina, 
in  the  United  States.  The  colours  often  resemble  Sapphire, 
but  Cyanite  is  softer  and  less  dense. 

403.  EUCLASE. 

Euclase  is  a  rare  mineral,  occurring  in  crystals  of  a  green 
or  greenish  blue  colour,  often  transparent,  and  having  a 
vitreous  lustre.  It  is  doubly  refracting,  though  only  in  a 
feeble  degree,  the  greatest  and  least  indices  for  yellow  light 
being  1'671  and  1*652.  The  dispersion  is  also  small,  but 
there  is  a  distinct  pleochroism.  It  is  easily  electrified  by 
friction,  and  on  strongly  heating  gives  off  water.  The 
specific  gravity  is  3*05  to  3'10.  It  is  brittle,  shows  a  con- 
choidal  fracture,  and  has  three  cleavages  parallel  to  the 
three  primary  crystal  forms.  It  occurs  in  short  monosym- 
metric  prisms  vertically  striated,  the  crystals  often  being 
highly  modified. 

In  composition  it  is  a  hydrated  beryllium  aluminium 
silicate,  H20,  2  BeO,  A1203,  2  Si02. 

It  occurs  in  chlorite  schist  near  Novas  Minas,  in  Brazil, 
with  yellow  Topaz ;  also  near  the  Sanarka  Eiver,  in  the 
Urals,  in  gold-bearing  alluvium,  with  Topaz  and  Corundum. 
It  has  also  been  found  in  very  small  crystals  in  the 
Alps. 

It  maybe  distinguished  from  Beryl  (variety Aquamarine) 
by  being  of  higher  specific  gravity,  and  more  strongly 
dichroic,  and  from  blue  Topaz  by  being  less  dense  and 
more  dichroic. 


PKECIOUS  STONES.  271 

407.  EPIDOTE. 

Epidote,  like  Cyanite  and  Andalusite,  is  of  wide  distribu- 
tion, but  is  rarely  found  of  a  kind  suitable  for  use  as  a  gem. 
The  colour  is  characteristically  pistachio-green,  merging  to 
a  yellow-green  and  clear  yellow,  or  to  a  brownish  green  or 
green-black ;  rarely  colourless  or  red.  It  has  a  vitreous 
lustre,  and  when  cut  as  a  gem  is  very  brilliant.  The  gem 
variety  is  transparent,  but  the  common  varieties  are  found 
quite  opaque  sometimes.  It  is  strongly  refracting,  and  the 
double  refraction  is  very  marked  too,  the  greatest  and  least 
indices  for  red  light  being  1*768  and  T730.  Pleochroism  is 
unusually  well  marked,  showing  tints  of  green,  brown  and 
yellow  in  three  different  directions.  The  specific  gravity  is 
3*35  to  3*5.  The  mineral  is  brittle,  and  has  an  uneven 
fracture ;  it  shows  two  cleavages,  one  perfect  and  the 
other  imperfect.  It  crystallises  in  monosymmetric  forms, 
usually  prismatic,  sometimes  acicular.  It  is  often  found  in 
attached  crystals  in  cavities,  usually  in  thermo-metamorphic 
rocks.  Its  common  associates  are  Calcite,  Apatite,  Felspar, 
and  Asbestos.  In  composition  it  is  a  silicate  of  calcium 
and  aluminium,  with  iron,  containing  some  water, 
H20,  4  CaO,  3  (Al,  Fe)203,  6  Si02 ;  the  water  is  driven  off 
on  strongly  heating.  The  chief  locality  is  Knappenwand, 
in  the  Untersulzbachthal  in  Salzburg,  where  it  occurs  in 
an  epidote-schist.  It  is  also  found  in  the  United  States  at 
Haddam  in  Connecticut ;  at  Eoseville  in  Sussex  County, 
New  Jersey ;  and  in  Georgia.  Some  Epidote  of  gem  quality 
has  been  found  in  Brazil,  with  green  Tourmaline  in  Minas 
Geraes. 

It  is  distinguished  from  most  similarly  coloured  minerals 


272 


PKECIOUS  STONES. 


by    its    greater    density    and     more    marked    dichroism. 
Tourmaline,  which  is  strongly  dichroic,  is  much  less  dense. 

410.  AXINITE. 

Axinite  is  but  rarely  used  as  a  gem,  although  it  has 
many  properties  making  it  suitable  for  such  a  use.  In 
colour  it  varies  from  a  pale  sherry  yellow  to  a  deep  brown 


FlG.  38. — A  Group  of  Axinite  Crystals. 

or  almost  plum  colour ;  the  usual  tint  is  clove  brown. 
The  lustre  is  vitreous,  inclining  to  adamantine  in  some 
specimens,  and  the  crystals  are  often  transparent.  It  is 
doubly  refracting,  the  indices  in  red  light  being,  the 
greatest  1*681,  and  the  least  T672.  It  shows  marked 
dichroism,  yielding  olive  green  and  violet-blue,  or  cinnamon 
brown  and  violet-blue  images  in  the  dichroscope,  according 
to  the  direction  in  which  the  crystal  is  viewed.  It  is  pyro- 


PKECIOUS   STONES.  273 

electric,  and  readily  fuses.  The  specific  gravity  is  3*29  to 
3'30.  It  is  very  brittle,  has  a  hardness  of  6J  to  7,  and 
shows  several  planes  of  cleavage.  The  streak  is  colourless. 
It  crystallises  in  thin  triclinic  prisms,  having  thin  edges 
and  being  somewhat  axe  shaped  (Fig.  38),  hence  the  name 
(from  a£ivrj).  In  chemical  composition  it  is  a  boro-silicate 
of  aluminium  and  calcium  with  iron  and  manganese,  the 
latter  metals  probably  accounting  for  the  colour.  It  is 
found  at  St.  Christophe,  in  Dauphine,  in  gneiss,  and  in 
the  east  of  Switzerland,  near  Dissentis,  as  well  as  in  several 
less  important  localities.  It  may  readily  be  distinguished 
by  its  colour  and  appearance  in  the  dichroscope. 

411.  PBEHNITE.  , 

Prehnite,  although  not  itself  a  Zeolite,  is  in  many  respects 
closely  allied  with  the  Zeolites  in  mode  of  formation  and 
occurrence.  It  is  found  in  a  great  range  of  colours,  some 
of  them  very  beautiful.  Usually  the  colour  is  some  tint  of 
green,  but  occasionally  it  passes  to  a  brilliant  orange  or  a 
pale  pink  ;  other  specimens  are  colourless.  It  is  mostly 
subtransparent  to  translucent,  with  a  vitreous  lustre.  It  is 
doubly  refracting,  the  mean  index  being  T626,  and  shows 
rather  strong  dispersion ;  but  individual  crystals  are  rare, 
and  usually  small,  the  material  used  as  a  precious  stone 
being  a  crystalline  aggregate.  It  is  pyro-electric ;  the 
specific  gravity  is  2*92  to  3*01,  and  the  hardness  is  6  to  6j. 
The  crystalline  form  is  orthorhombic.  It  usually  occurs  in 
aggregates  of  minute  indistinct  crystals  strongly  coherent, 
and  is  found  sometimes  in  large  masses,  one  in  the  Heddle 
collection  in  the  Eoyal  Scottish  Museum  measuring  3  feet 
in  length.  It  is  always  found  as  a  product  of  the 

p.s,  T 


274  PKECIOUS  STONES. 

decomposition  of  more  or  less  basic  eruptive  rocks.  It  is 
an  acid  calcium  aluminium  orthosilicate,  H2Ca2Al2Si3Oi2.  It 
is  found  in  many  parts  of  Scotland,  as  Dumbartonshire  and 
Eenfrewshire ;  also  with  the  last  mentioned  species,  Axinite, 
at  St.  Christophe  in  Dauphine,  at  several  places  in  the 
Alps,  at  Ala  in  Piedmont,  and  in  Cape  Colony  ("  Cape 
Chrysolite").  In  the  United  States  it  is  found  in  the 
Lake  Superior  copper  region  with  Native  Copper,  at 
Farmington  in  Connecticut,  and  at  Bergen  Hill  in  New 
Jersey.  Prehnite  is  rather  apt  to  lose  its  colour  on  exposure. 

426.  TOURMALINE. 

Tourmaline  is  almost  as  remarkable  as  Corundum  for  the 
number  of  colour  varieties  which  are  used  as  gems,  and  as 
with  Corundum,  too,  these  gem  varieties  are  rarely 
associated  with  the  name  of  the  mineralogical  species  to 
which  they  belong.  Tourmaline  most  commonly  occurs 
black,  but  such  specimens  are  not  used  as  gems.  The 
various  shades  of  red,  blue  and  green,  in  which  the  mineral 
is  found,  are  all  to  be  seen  in  cut  specimens  ;  more  rarely 
the  colourless  variety  is  cut.  Only  the  transparent  forms 
are  used,  and  these  have  a  vitreous  lustre.  The  mineral  is 
doubly  refracting,  but  the  indices  are  not  high,  though 
there  is  a  relatively  considerable  difference  between  the 
ordinary  and  extraordinary  rays,  the  values  of  the  indices 
for  yellow  light  being  (in  a  colourless  specimen)  T637  and 
1*619.  The  dichroism  is,  however,  very  marked,  more  so 
than  in  any  other  precious  stone  except  lolite.  The  images 
in  the  dichroscope  are  usually  of  nearly  the  same  colour  as 
the  crystal,  but  they  differ  greatly  in  depth,  and  sometimes 
to  some  extent  in  tint;  crystals  of  the  green  and  blue 


PEECIOUS  STONES. 


275 


shades  of  Tourmaline  are  particularly  dichroic.  The 
electrical  properties  are  equally  well  marked ;  thus  rubbing 
induces  a  difference  of  electric  potential,  and  heat  produces 
a  marked  difference,  one  end  of  the  crystal  becoming  positive 
and  the  other  negative,  so  that  if  a  mixture  of  red  lead  and 
sulphur  be  dropped  on  to  a  heated  crystal  through  a  fine 
sieve  the  sulphur  will  be  attracted  to  one  end  (the  positive) 
and  the  red  lead  to  the  other  (the  negative) ;  this  readily 
distinguishes  the  two  ends ;  the  electrical  properties  are 
in  some  cases  of  value  in  identifying 
Tourmaline.  ,  The  specific  gravity 
varies  from  2*98  to  8'20,  but  most 
of  the  gem  varieties  have  a  nearly 
constant  density,  as  will  be  noted 
below.  The  mineral  is  brittle  and 
has  a  subconchoidal  fracture.  Its 
hardness  is  7  to  7^.  There  are 

two  indefinite  cleavages  ;    the   streak  n 

FIG.  39.— Characteristic 

is  colourless.     In  crystalline  form  it  is     p0rm  of  Tourmaline, 
rhombohedral  and  is  hemimorphic,  but 

as  doubly  terminated  crystals  are  rare,  this  is  not  often  seen 
in  the  ends,  but  in  the  prism  faces  it  is  usually  apparent, 
for  the  crystal  in  section,  instead  of  being  hexagonal,  has 
the  form  of  a  modified  triangle  through  the  predominance 
of  alternate  faces  of  the  hexagonal  prism  (Fig.  39). 
Another  peculiar  feature  of  the  crystals  which  throws 
light  on  the  mode  of  origin  of  the  mineral  is  the  frequency 
with  which  the  prism  faces  are  well  developed  in 
comparison  with  the  terminal  planes.  The  crystals,  too, 
are  very  frequently  fractured  and  dislocated.  It  is  a 
mineral  of  secondary  origin  usually  found  in  association 

T  2 


276  PKECIOUS   STONES. 

with  rocks  that  have  been  subjected  to  dynamo-  (and 
in  many  cases  thermo-)  metamorphism.  Consistent 
with  this  we  find  the  mineral  often  shows  flaws  or 
"feathers,"  though  in  other  respects  it  is  remarkably  free 
from  imperfection.  The  pink  variety  is  very  frequently 
flawed  in  this  way  (Fig.  40). 

It  is  often  found  associated  with  Quartz,  Albite,  Lepidolite, 


FIG.  40. — Tourmaline  in  the  Matrix. 

Beryl,  Idocrase,  Garnet,  Spinel,  Cassiterite,  Talc,  Rutile, 
Chrysoberyl,  etc. 

The  varieties  are  mostly  classified  according  to  colour. 
The  common  black  type  is  known  as  Schorl ;  a  black  variety 
from  Kragero  in  Norway  is  known  as  Aphrizite.  The  red 
colours  are  comprised  under  Rubellite,  the  violet-red  speci- 
mens from  Siberia  being  called  Siberite.  Rubellite  has  a 
specific  gravity  of  3'08.  Indicolite  (or  Indigolite)  includes 
the  blue  shades  (density  3'16),  the  deeper  Berlin-blue 
crystals  from  Brazil  being  called  Brazilian  Sapphire,  The 


f&ECIOUS  STONES.  277 

green  forms  include  a  bright  green  from  Brazil  called 
Brazilian  Emerald,  and  a  softer  yellow-green  type  found  in 
Ceylon  and  known  as  Ceylonese  Chrysolite  or  Ceylonese 
Peridot.  Green  Tourmaline  has  a  specific  gravity  of  3*107. 
The  colourless  variety  is  known  as  Achroite,  and  has  a 
specific  gravity  of  3*022.  Dravite  is  a  brown  Tourmaline 
from  Carinthia. 

In  chemical  composition  Tourmaline  is  very  varied,  and 
in  fact  it  may  be  regarded  rather  as  an  isomorphous  series. 
It  is  essentially  a  silicate  of  boron  and  aluminium,  but 
water  and  fluorine,  as  well  as  the  alkali  metals,  and  the 
elements  titanium,  iron,  manganese,  magnesium,  and 
calcium  may  be  present.  No  exact  molecular  formula  has 
ever  been  arrived  at ;  as  with  many  other  minerals,  an 
increase  in  the  percentage  of  iron  present  is  accompanied 
by  a  greater  depth  of  colour. 

The  localities  where  Tourmaline  occurs  are  so  numerous 
that  only  the  places  where  material  suitable  for  gem  use, 
or  where  exceptionally  coloured  specimens  are  found,  can  be 
given . 

In  the  Ural  Mountains,  in  the  neighbourhood  of  Mur- 
sinka,  Eubellite  is  found  in  granite ;  the  blue  Indicolite  also 
occurs  here,  and  Kubellite  in  the  Nerchinsk  district  of 
Trans-Baikalia. 

In  Brazil  in  the  Novas  Minas  district  and  in  the  Kibeirao 
da  Tolha  green  Tourmaline  is  found,  some  of  it  being  the 
bright  green  known  as  Brazilian  Emerald ;  the  blue  variety 
"  Brazilian  Sapphire,"  and  a  little  Eubellite  also  are  found 
here. 

The  gem  gravels  of  Ceylon  yield  the  yellow  and  yellow- 
green  stones  known  as  Ceylonese  Chrysolite  (or  Peridot)' 


278  PKECIOUS 

and  the  brown  Tourmaline  occurs  with  them.  In  Bengal, 
and  in  the  Sapphire  deposits  of  Kashmir,  Indicolite  is  found, 
and  Eubellite  occurs  near  Mainglon  in  Burma. 

In  the  island  of  Elba,  near  San  Piero,  both  the  colourless 
Acroite  and  the  red  Kubellite  are  found  in  granite,  and 
Eubellite  is  found  at  Penig  in  Saxony,  with  green  and  blue 
varieties.  Dravite  is  named  after  its  locality  at  the  Unter- 
drauburg  in  the  Drave  district  of  Carinthia.  It  is  also  found 
at  Crawford  in  New  York  State,  while  in  the  same  State,  in 
St.  Lawrence  County,  fine  Achroite  occurs  near  De  Kalb. 
In  Maine  at  Paris  the  green  variety  as  well  as  Kubellite 
and  Indicolite  occur ;  in  Massachusets,  Chesterfield  and 
Goshen  yield  good  Indicolite  and  green  Tourmaline,  and 
also  a  rose-red  but  opaque  variety ;  in  California,  at  Mesa 
Grande,  both  the  red  and  green  varieties  occur. 

The  technical  use  of  Tourmaline  in  the  construction  of 
plates  for  the  polariscope  should  be  mentioned ;  the  slices 
are  cut  from  the  crystal  parallel  to  the  vertical  axis. 

In  cutting  Tourmaline  as  a  gem  due  regard  must  be  given 
to  the  colour  effect  from  the  pleocroism.  Deep  coloured 
stones  are  cut  so  as  to  have  the  table  parallel  to  the  vertical 
axis ;  but  in  the  case  of  pale  stones  the  table  may  be  normal 
to  this  axis,  for  in  this  direction  the  mineral  shows  its 
darkest  colour.  Tourmaline  is  often  parti-coloured,  one 
end  of  a  crystal  may  be  green,  and  this  may  gradually 
merge  into  pink  at  the  other  end,  being  accompanied  prob- 
ably by  a  corresponding  gradual  change  from  a  Tourmaline 
of  one  composition  to  one  of  another.  The  Eubellite  from 
Paris  in  Maine  often  shows  an  outer  green  layer ;  a  certain 
amount  of  Eubellite  has  crystallised  first,  and  then  the 
isomorphous  green  Tourmaline  has  been  deposited  in  optical 


PEECIOTJS  STONES.  279 

continuity  with  it ;  this  may  be  compared  with  the  well- 
known  double  growths  of  common  alum  and  chrome-alum. 
Eubellite  is  apt  to  appear  of  a  brown  colour  in  artificial 
light.  Coloured  Tourmaline  is  usually  cut  in  steps  or  as  a 
table,  and  the  appearance  is  often  improved  by  the  gem 
being  set  in  a  closed  mount  with  foil. 

Tourmaline,  although  in  its  various  colours  it  so  closely 
resembles  in  outward  appearance  so  many  other  gems,  may 
in  most  cases  be  identified  by  its  specific  gravity  alone. 
Thus  Aquamarine,  Emerald,  and  Beryl  generally,  Quartz 
and  Phenakite  are  all  less  dense.  Hiddenite  is  slightly 
more  dense,  while  Corundum  in  all  its  varieties,  Garnet  in 
its  different  forms,  Olivine,  Topaz,  Spinel,  Zircon,  and 
Diamond  are  all  of  distinctly  greater  specific  gravity. 
Further,  the  green  and  blue  kinds  of  Tourmaline  are  very 
markedly  dichroic,  and  this  aids  in  the  further  differentia- 
tion of  the  green  Hiddenite.  The  similarity  of  the  coloured 
images  seen  in  Tourmaline  under  the  dichroscope,  and  its 
marked  electrical  properties  are  additional  points  of 
distinction. 

428.  STAUROLITE. 

Staurolite  suitable  for  gem  use  occurs  but  sparingly,  and 
it  is  a  mineral  but  little  used  for  this  purpose.  What  is  so 
used  is  a  reddish-brown,  sometimes  inclining  to  claret, 
and  is  transparent,  though  the  ordinary  forms  are  only 
translucent  to  opaque.  The  mineral  shows  double  refrac- 
tion (the  greatest  and  least  indices  being  1'746  and  1*736) 
and  is  distinctly  pleochroic,  being  hyacinth-red  in  one 
direction  and  yellow-red  in  the  other  two  directions.  The 
specific  gravity  is  3*73  to  3'75,  and  the  hardness  7£.  The 


280  PBECIOUS  STONES. 

fracture  is  sub-conchoidal ;  it  shows  two  cleavages,  neither 
very  distinct.  The  crystals  belong  to  the  orthorhombic 
system,  and  are  often  twinned  in  crossed  forms  ;  hence  the 
name.  It  occurs  in  crystalline  rocks  as  a  product  of  con- 
tact metamorphism,  and  is  often  associated  with  Garnet 
and  Tourmaline.  In  chemical  composition  it  is  a  complex 
silicate  of  iron,  magnesium  and  aluminium.  It  occurs  in 


EJG.  41. — Precious  Serpentine  (Polished). 

schist  at  Monte  Campione  in  Switzerland,  and  with 
Corundum  in  Macon  County  in  North  Carolina,  in 
the  United  States.  When  used  as  a  gem  it  is  cut 
en  cabochon. 

481.  SERPENTINE. 

It  is  rather  questionable  if  the  material  used  for  the  pro- 
duction of  plaques,  vases,  and  other  similar  ornamental 
objects  should  not  be  regarded  rather  as  a  rock  than  as  a 


PBECIOUS  STONES,  281 

mineral,  as  it  occurs  in  large  masses  and  often  includes 
other  minerals.  The  form  so  used,  however,  has  fairly 
definite  physical  and  chemical  properties,  and  contains  a 
very  large  percentage  of  one  compound.  Such  Precious  or 
Noble  Serpentine  is  of  a  rich  oil  green  to  pistachio  green, 
markedly  translucent,  with  a  waxy  lustre;  its  specific 
gravity  is  2*5  to  2*6,  and  its  hardness  barely  equal  to  3.  It 
is,  however,  capable  of  taking  a  high  polish.  It  shows  no 
crystalline  form,  being  always  massive  (Fig.  41).  It  is 
usually  a  hydration  product  of  ferro-magnesian  silicates,  and 
it  is  itself  a  hydrated  silicate  of  magnesium,  H4Mg3Si209. 
It  is  found  in  Cornwall,  in  the  Isle  of  Man,  and  at  Portsoy, 
in  Britain  ;  at  Falun  in  Sweden  ;  in  Saxony,  Siberia,  etc. 

510.  SPHENE. 

Sphene  is  only  used  as  a  gem  when  it  occurs  transparent, 
and  of  a  good  colour.  The  colour  may  be  green,  brown, 
yellow,  or  rose  red ;  the  lustre  is  adamantine.  It  shows 
double  refraction,  the  greatest  index  being  2*01  for  yellow 
light,  and  the  dispersion  is  very  large.  It  is  markedly 
pleochroic,  showing  red,  greenish-yellow,  and  almost  colour- 
less images,  according  to  the  direction  in  which  it  is 
examined.  The  specific  gravity  is  3*35  to  3*45,  and  the 
hardness  5  to  5J.  It  shows  several  cleavages,  none  very 
well  marked.  In  crystalline  form  it  is  monosymmetric,  and 
it  is  usually  found  in  embedded  idiomorphic  crystals  of 
a  wedge  shape,  as  an  original  constituent  of  granites  and 
similar  rocks,  but  it  may  occur  as  a  product  of  thermo- 
metamorphism.  Crystals  suitable  for  gem  use  are  usually 
attached  to  the  sides  of  cavities  in  these  rocks.  In  com- 
position it  is  a  titano-silicate  of  calcium,  CaTiSiOg. 


282  PRECIOUS  STONES. 

Crystals  up  to  2J  inches  long  suitable  for  gem  use  have 
been  found  near  Bridgewater  Station,  in  Delaware  County 
in  Pennsylvania ;  good  specimens  are  also  obtained  from 
the  Alps.  All  the  gem  stones  it  may  resemble  are  harder 
than  Sphene. 


CHAPTEE  XIV. 

549.    APATITE JET. 

APATITE  occurs  in  a  variety  of  colours  that  may  give  it, 
when  cut,  an  appearance  similar  to  several  other  minerals 
used  as  gems.  The  usual  colour  is  a  pale  green,  but  blue, 
violet,  red,  yellow,  and  brown  are  sometimes  seen  in  this 
species.  It  is  transparent  to  opaque,  but  the  transparent 
kinds  are  the  only  ones  used  for  cutting.  The  lustre  is 
vitreous,  and  the  mineral  shows  weak  double  refraction, 
the  indices  for  yellow  light  being  1*646  and  1*642;  it  shows 
pleochroism  in  the  more  deeply  coloured  specimens.  Some- 
times a  chatoyant  reflection  is  seen  on  the  basal  plane. 
The  specific  gravity  is  3*16  to  3 '22  ;  the  mineral  is  brittle, 
shows  a  conchoidal  fracture,  and  has  two  imperfect  cleavages, 
one  parallel  to  the  basal  plane,  and  the  other  a  prismatic 
cleavage.  It  occurs  in  crystals,  often  highly  modified, 
belonging  to  the  hexagonal  system.  It  is  a  calcium  phos- 
phate, with  fluorine  or  chlorine,  [Ca  (F,C1)]  Ca4P3Oi2.  It 
is  found  in  good  specimens  at  Ehrenfriedersdorf  in  Saxony  ; 
pale  yellow  and  pale  green  crystals  occur  in  the  Zillerthal, 
and  in  Mosedale  in  Cumberland  ;  the  deep  green  variety  is 
found  at  Arendal  in  Norway,  in  Siberia,  and  in  Canada. 
Canada  also  yields  a  rose  red  type  at  St.  Eoch ;  and  red  and 
green  crystals  are  found  at  Auburn  in  Maine  in  the  United 
States.  Its  specific  gravity  and  softness  distinguish  it  from 


284  PRECIOUS  STONES. 

most  minerals  with  which  it  may  be  confused.     The  double 
refraction  differentiates  it  from  Fluor  Spar. 

642.  TURQUOIS. 

This  may  have  been  the  Callais  of  Pliny,  but  King  refers 
Pliny's  Callina  to  the  coarser  forms  of  Olivine.  It  seems, 
too,  to  have  been  much  used  by  the  ancient  Persians  as  one 
of  the  stones  known  as  Smaragdus;  there  were  many 
curious  superstitions  connected  with  it,  such  as  its  power 
of  preserving  the  bones  of  the  human  body  from  fracture 
due  to  a  fall,  if  the  person  who  fell  was  wearing  one  of  these 
gems ;  it  was  the  gem  which  broke  instead  of  the  bone. 

It  occurs  in  various  shades  of  green  and  blue,  sometimes 
rather  grey  or  white.  The  most  valued  colours  among 
Western  races  are  the  rich  sky  blue,  but  among  many  of 
the  Eastern  people  the  more  abundant  green  shades  are 
preferred.  It  is  feebly  translucent,  and  in  very  thin  slices 
may  be  transparent.  Its  lustre  is  vitreous  to  waxy,  and 
dull.  Although  always  massive  it  may  show  double  refrac- 
tion, and  hence  is  not  amorphous ;  it  is  more  likely  that  it 
is  cryptocrystalline  like  Chalcedony.  The  specific  gravity 
is  2*62  to  3*0,  the  fracture  subconchoidal,  and  the  hardness 
equal  to  6.  There  is,  of  course,  no  cleavage;  the  streak 
is  white  or  pale  green.  It  always  occurs  as  a  deposition 
from  percolating  water,  thus  usually  in  crevices  and  cavities 
in  rocks  that  are  somewhat  decomposed.  It  may  fill  the 
crevice,  or  may  form  a  thin  layer  on  the  sides  only.  It 
seems  often  to  result  from  the  weathering  of  Felspar  and 
Apatite,  and  has  been  found  pseudomorphous  after  both 
these  minerals,  after  Felspar  in  Persia,  and  after  Apatite  in 
California. 


PRECIOUS   STONES.  285 

In  composition  it  is  a  hydrous  phosphate  of  aluminium, 
iron  and  copper,  and  the  formula  [A1(OH)2,  Fe(OH)2 
Cu(OH)H]3P04  has  been  suggested  by  Penfield,  who 
believes  the  copper  and  iron  to  be  essential  constituents. 
The  colour  is  probably  due  to  these  metals  in  vary- 
ing proportion.  It  is  infusible  before  the  blowpipe,  but 
on  heating  it  decrepitates  and  gives  off  water.  Most 
varieties  are  soluble  in  the  mineral  acids.  Many  speci- 
mens are  found  to  lose  their  colour  after  a  time,  possibly 
owing  to  a  spontaneous  dehydration. 

The  most  important  locality  is  Persia,  where  it  occurs  in 
volcanic  rocks  intrusive  into  various  sedimentary  rocks  in 
the  Khorassan  province,  at  the  village  of  Maden,  associated 
with  Limonite.  These  mines  were  mentioned  by  Ben  Mansur 
(1300),  who  also  gives  as  localities  for  Turquois,  Ghasna, 
Kerman  and  Irak.  The  material  is  not  only  found  in  situ, 
but  also  in  detritus  derived  from  these  volcanic  rocks,  and 
in  this  debris  some  of  the  finest  specimens  are  found.  In 
addition  it  occurs  at  several  other  places  in  Persia. 

In  the  Sinai  Peninsula  it  is  found  in  the  Wadi  Meghara 
in  mines  that  have  been  worked,  it  is  supposed,  since 
3000  B.C.  In  the  Kirghiz  Steppes  it  is  found  of  a  greenish 
blue  colour.  Also  in  the  Kara-Tube  Mountains  in  a 
siliceous  rock,  with  Limonite.  In  the  United  States  it  is 
found  at  several  places  in  New  Mexico,  and  in  all  of  these 
it  seems  to  have  been  worked  in  remote  times  by  the 
ancient  Mexican  races ;  one  of  the  principal  places  there  is 
Mount  Chalchuitl  in  the  Los  Cerillos  Mountains ;  another 
is  in  the  Burro  Mountains.  In  Nevada  it  is  found  north 
of  Columbus ;  also  in  Arizona  and  California. 

Most  of  the  searching  for  the  material  is  now  done  in 


286  PRECIOUS   STONES. 

open  workings,  but  when  the  Persian  mines  were  under  the 
government  of  that  country  systematic  working  underground 
was  carried  out,  and  there  are  extensive  underground 
workings  in  New  Mexico  as  well  as  huge  heaps  of  debris  on 
the  surface. 

When  cut  as  a  gem,  it  is  either  en  cabochon  or  in  a  flat 
elliptical  plate.  The  colour  is  sometimes  artificially 
intensified  by  Berlin-blue.  Turquois  shows  its  colour  well 
at  night,  while  most  of  its  imitations  appear  less  beautiful 
in  artificial  light.  The  best  specimens  are  known  as 
Oriental  Turquois  or  "stones  of  the  old  rock."  The  value 
now  is  not  so  great  as  it  was  at  one  time,  but  good  specimens 
find  a  ready  market,  and  on  account  of  the  difficulty  in 
obtaining  large  perfect  pieces  the  value  rises  rapidly  with 
the  increase  of  weight. 

746.  GYPSUM.  . 

Gypsum  is  only  used  in  its  finely  fibrous  variety,  Satin 
Spar,  and  massive  variety  Alabaster.  Alabaster  does  not 
seem  to  have  been  included  in  Pliny's  Alabastrites,  though 
the  fibrous  and  the  stalactitic  varieties  of  carbonate  of  lime 
were.  King  identifies  the  Lygdinus  with  compact  Gypsum 
or  Alabaster. 

Gypsum  occurs  colourless,  white,  pink,  blue,  brown  and 
yellow.  Some  forms  show  banding  of  different  colours.  It 
is  transparent  to  subtranslucent ;  the  lustre  is  vitreous  to 
pearly  ;  in  Satin  Spar  it  is  silky.  On  heating,  water  is  given 
off  and  the  mineral  becomes  opaque.  The  specific  gravity 
is  2*28  to  2*33,  the  hardness  2.  The  mineral  crystallises  in 
monosymmetric  forms,  and  there  is  one  distinct  cleavage 
and  two  indistinct  ones.  In  chemical  composition  it  is 


PKECIOUS  STONES.  287 

a  hydrous  sulphate  of  calcium,  CaS04,  2H20.  It  occurs 
frequently  in  connection  with  sedimentary  deposits  laid 
down  in  closed  areas  of  water ;  Alabaster  is  often  found  in 
irregular  beds,  and  Satin  Spar  in  veins,  in  marls  with  such 
a  history,  as  in  those  in  Cumberland,  Westmorland  and 
Nottingham.  Very  fine  massive  Gypsum  is  found  at 


FIG.  42. — Gypsum ;  variety  Satin  Spar. 

Castelino,  35  miles  from  Leghorn.     Fig.  42  shows  a  vein  of 
Satin  Spar. 

AMBER. 

Amber  is  not  strictly  speaking  a  mineral,  being  of  organic 
origin. 

It  is  found  in  irregular  masses  of  a  yellow  brown  or 
reddish  shade,  showing  a  conchoidal  fracture  but  no  cleav- 
age. It  is  transparent  to  translucent  and  opaque,  with  a 
specific  gravity  of  1*05  to  1*10,  and  a  hardness  of  2  to  2J ; 
the  lustre  is  resinous.  On  heating  it  softens  and  then 
melts.  The  ancients,  who  called  Amber  Electrum,  noticed 


288  PKECIOUS   STONES. 

the  property  it  had  of  attracting  small  bodies  to  itself  when 
rubbed.  From  this  property  of  Amber  our  word  Electricity 
is  derived.  The  substance  was  also  known  as  Succinum 
and  Lyncurium  in  Pliny's  time,  and  is  still  spoken  of  as 
Succinite.  The  electrical  charge  is  negative. 

In  origin  Amber  is  the  fossilised  resin  of  certain  plants ; 
at  the  time  when  it  was  viscous  flies  often  became  attached 
to  it,  and  in  their  endeavours  to  escape  have  sometimes 
damaged  themselves,  so  that  a  leg  of  a  fly  may  be  found 
enclosed  in  Amber  a  little  distance  from  where  the  fly  is. 
Apart  from  these  inclusions  most  varieties  of  Amber — all 
but  the  "  water-clear "  in  fact — show  numerous  minute 
bubbles ;  the  smaller  the  bubbles  the  more  numerous  they 
are,  and  thus  the  more  cloudy  the  specimen  seems.  Such 
cloudy  material  may  be  clarified  by  gradually  heating  the 
Amber  in  an  oil  of  nearly  the  same  refractive  index,  which 
is  about  1*53.  Eape  seed  oil  is  usually  used  ;  it  gradually 
permeates  all  the  minute  pores  and  removes  the  disturbing 
cause  very  largely. 

In  composition  Amber  is  an  oxygenated  hydrocarbon 
having  the  empirical  formula  CioHi60. 

Amber  is  chiefly  found  on  the  seaboard  of  the  Baltic, 
where  after  storms  it  is  picked  up  on  the  shore ;  it  is  also 
dredged  for  in  the  sands  of  the  shallows.  It  is  found,  too, 
along  the  coasts  of  Jutland  and  Schleswig-Holstein.  In 
the  south  and  east  of  England,  in  Western  Eussia,  in  parts 
of  Poland,  in  Spain  and  Sicily,  Amber  is  found  in  sandy 
deposits.  One  piece  in  the  Imperial  Museum  in  Berlin 
weighs  eighteen  pounds. 

Amber  of  inferior  quality  is  used  in  the  manufacture  of 
some  varnishes,  and  small  pieces  are  now  hydraulically 


PBECIOUS   STONES.  289 

compressed  when  soft  into  flat  pieces  known  as  Spiller 
imitations ;  it  then  shows  several  peculiarities,  such  as 
streaks,  a  sharp  demarcation  between  clear  and  cloudy 
portions,  and  microscopically  the  cavities  show  signs  of 
deformation. 

Amber  is  largely  worked  into  beads,  mouth-pieces 
for  pipes  and  cigarette-holders,  walking  stick  knobs,  and 
the  like.  Sometimes  it  is  cut  and  polished  to  mount  in  a 
brooch.  It  can  be  easily  worked  in  a  lathe  and  can  be 
rendered  temporarily  flexible  by  heat. 

Celluloid  imitations  (Ambre  antique)  show  the  sharp 
demarcation  between  clear  and  cloudy  parts  as  in  pressed 
amber ;  the  smell  of  camphor  may  be  elicited  on  rubbing. 
Celluloid  is  rather  sectile. 

JET. 

Jet  is  a  dense  compact  variety  of  coal,  near  Cannel  Coal 
and  Lignite.  It  shows  no  microscopic  vegetable  structure, 
and  for  the  purposes  of  cutting  it  must  be  free  from  Iron 
Pyrites.  It  is  a  dense  black  in  colour,  and  opaque.  When 
polished  it  has  a  brilliant  lustre,  but  an  unpolished  surface 
is  glistening  or  even  rather  greasy  in  lustre.  The  fracture 
is  conchoidal.  The  specific  gravity  is  1*35  and  the  hardness 
3  to  4.  On  heating  it  burns  readily,  with  a  sooty  flame.  It 
is  found  in  flat  pieces  in  Liassic  rocks  at  Robin  Hood's 
Bay,  near  Whitby,  in  England,  and  in  other  parts  of  East 
Yorkshire  ;  in  France  in  the  province  of  Languedoc ;  in 
Asturia  in  Spain ;  in  Hesse  ;  the  Erzgeberg,  Bavaria,  and 
other  parts  of  Central  Europe.  In  America  fine  material  is 
found  in  Colorado. 

It  is  largely  used  for  mourning  ornaments  and  for   the 
p.s.  u 


290  PRECIOUS   STONES. 

manufacture  of  articles  such  as  beads,  trays,  small 
boxes,  etc.  It  can  be  fashioned  in  much  the  same 
way  as  hardwood  or  ivory,  but  the  final  polishing  is  done 
by  hand.  Much  of  the  working  of  Jet  is  carried  on  at 
Whitby. 


GLOSSARY. 


ABSOEPTION  BANDS. — The  absorption  bands  of  a  substance  are 
dark  bands  seen  in  the  spectroscope  when  the  substance 
is  interposed  between  a  source  of  white  light  and  the 
instrument. 

AGGLOMERATE. — A  rock  filling  the  vent  of  a  volcano  and  com- 
posed of  large  fragments  ejected  by  the  volcano. 

ALLOTEIOMOBPHIC  MINERALS. — Minerals  with  forms  other  than 
their  own  proper  form.  Due  to  pressure  of  surrounding 
bodies. 

ALLOTROPISM. — An  element  is  allotropic  when  it  occurs  in 
several  distinct  forms  without  change  of  chemical  compo- 
sition :  for  instance,  red  and  yellow  phosphorus,  or  carbon 
as  Graphite  and  Diamond. 

ANHYDROUS. — Without  water. 

AQUEOUS  THEORY. — A  theory  which  maintains  that  all  minerals 
were  deposited  from  a  simple  solution,  comparable  to  the 
deposition  of  crystals  of  saltpetre  from  a  solution  in 
water. 

ASTERISM. — The  property  of  exhibiting  a  star-like  light. 

BASAL  PLANE. — A  plane  on  the  termination  of  a  crystal,  cutting 
the  principal  axis  at  unit  length  and  lying  parallel  to  the 
other  axes. 

BASIC  EOCKS. — Eocks  containing  a  low  proportion  of  silica. 

BIAXIAL  CRYSTALS  show  three  directions  of  optical  elasticity, ' 
and  hence  have  three  indices  of  refraction.     All  crystals  of 
the  orthorhombic,    monosymmetric  and  triclinic  systems 
are  biaxial.     There  are  two  directions  in  which  light  travels 
with  equal  velocity. 

BOTRYOIDAL. — Like  a  bunch  of  grapes. 

u  2 


292  GLOSSABY. 

CAEAT. — The  unit  of  weight  for  gems ;  from  Kcpartov,  one  of  the 
vetches,  the  seeds  of  which  were  used  as  weights  in 
ancient  times,  on  account  of  their  uniform  size.  It  is 
equivalent  to  3-16  grains,  about  -2055  gram. 

COEFFICIENT  OF  EXPANSION. — The  increment  by  which  a  sub- 
stance of  unit  size  increases  its  size  (at  0°  C.)  for  an 
increase  of  one  degree  of  temperature. 

COLLOID. — A  substance  having  no  crystalline  structure ;  on 
account  of  difficulty  of  absolutely  determining  this  a  colloid 
is  now  often  regarded  as  a  substance  having  a  molecular 
weight  greater  than  a  certain  figure. 

CONDUCTIVITY  OF  HEAT. — The  conductivity  of  a  substance  is 
the  amount  of  heat  that  will  pass  through  a  unit  area  of 
that  substance  of  unit  thickness  in  unit  time,  when  the 
difference  of  temperature  of  the  surfaces  is  1°  C. 

CONTACT  TWINS. — Crystals  showing  a  form  as  if  a  single  crystal 
had  been  divided  in  two  halves  and  one  half  rotated 
through  180°. 

CRYSTAL. — A  substance  of  definite  chemical  composition  having 
a  definite  internal  molecular  arrangement  and  a  definite 
external  form,  bounded  by  plane  surfaces,  systematically 
arranged  and  meeting  in  angles  of  fixed  and  definite 
value. 

CRYSTALLINE. — Showing  the  internal  structure  of  a  crystal  but 
not  the  external  form. 

D  LINE. — A  brilliant  double  line  seen  in  the  yellow  portion  of 
the  spectrum,  characteristic  of  the  metal  sodium. 

DECREPITATION. — A  crackling  of  a  substance  when  heated,  due 
to  the  sudden  separation  of  particles. 

DENDRITIC. — In  tree-like  forms. 

DETRITUS. — Material  resulting  from  the  breaking  down  of  a 
rock  from  natural  causes. 

DIFFRACTION  GRATING. — A  piece  of  smooth  glass  or  metal  ruled 
with  fine  lines  of  equal  width  and  equidistant  from  one 
another  so  as  to  form  a  series  of  minute  rectangles.  The 
lines  may  be  up  to  43,000  to  an  inch,  usually  about  30,000. 
Such  a  grating  modifies  light  so  as  to  produce  a  spectrum. 


GLOSSAEY.  293 

DIHEDRAL  ANGLE. — The  angle  formed  by  the  meeting  of  two 

planes  in  an  edge. 
DIVIDED  ARCS. — Portions   of  a  circle,  usually  made  in  brass, 

graduated  into  units  and  fractions  of  angular  measurement. 
DODECAHEDRON. — A  form  of  the  cubic   system   having  twelve 

faces  each   the  shape  of  a  rhomb.     This  is  the  rhombic 

dodecahedron  (Fig.  23).     Other   twelve -faced   forms   also 

occur. 

DRUSE. — A  cavity  lined  with  crystals. 
DYNAMO-METAMORPHISM. — Change  induced  in  a  rock  as  a  result 

of  mechanical  movement.     Since  this  movement  usually 

occurs  under  great  pressure  it  is  usually  accompanied  by 

great  heat. 
ELECTROSCOPE. — An    instrument    for   detecting    an    electrical 

charge. 
EPIGENE  MINERALS. — Minerals    formed    from    others    by    the 

slow  downward    percolation  of  water  at  a  relatively  low 

temperature. 
ERUPTIVE  ROCKS. — Volcanic  rocks  which  have  been  poured  out 

on  the  surface  of  the  land  or  in  the  sea. 

FACET. — An  artificially  produced  plane  surface  on  a  gem  stone. 
FAULT. — A  surface  or  fissure  in  a  rock  mass  where  a  differential 

gliding  movement  has  occurred. 
FAULT  BRECCIA.—  A  mass  of  angular  fragments  of  rocks  lying 

in  a  fault  fissure. 
FERROMAGNESIAN  SILICATE. — A  mineral    consisting   largely  of 

silicate  of  iron  and  magnesium ;    usually  found  in  rocks 

containing  a  low  percentage  of  silica. 
FRITTING. — The  caking  of    the  ingredients  in    the   making  of 

glass. 
FUMAROLES. — Small  vents  around  a  volcano  from  which  gases, 

and  sometimes  mud,  escape  ;  often  found  on  volcanoes  of 

declining  activity. 

GEODE. — The  same  as  Druse  (q.  v.). 
GURGULHO. — A   deposit   of    angular   rock  fragments  in  which 

Diamonds  are  found. 
HABIT  (of  a  crystal). — A   term  used   to    indicate    the   general 


294  GLOSSAEY. 

form  of  a  crystal;  thus  one  of  a  "prismatic"  habit  is 
of  the  general  form  of  a  prism,  that  is,  more  or  less 
elongated. 

HEMIHEDRAL. — Having  only  half  the  full  number  of  crystal 
faces  developed. 

HEMIMORPHIC. — Having  the  opposite  ends  of  the  crystal 
terminated  by  dissimilar  faces. 

HALOGEN  COMPOUND.— A  chemical  compound  of  a  base  with 
chlorine,  bromine,  iodine  or  fluorine. 

HIGH  POTENTIAL. — Having  a  great  electrical  pressure  or 
electromotive  force. 

HYDROUS. — Containing  water. 

HYDRO-THERMAL  MINERAL. — One  whose  formation  is  due  to 
the  action  of  heated  water,  usually  acting  under  great 
pressure. 

HYPOGENE  MINERALS. — Minerals  arising  by  forces  acting  from 
within  the  earth  outwards. 

IDIOMORPHIC. — Having  the  form  proper  to  the  particular  sub- 
stance. Most  minerals  in  crystalline  rocks  that  are 
idiomorphic  have  crystallised  out  from  the  rock  magma 
at  an  early  stage  in  its  consolidation. 

INTERFERENCE  OF  LIGHT. — A  change  in  light  due  to  its  waves 
being  altered. 

INTERPENETRATION  TWINS. — Twinned  crystals  appearing  to 
have  much  of  their  substance  in  common,  but  with  the 
solid  and  dihedral  angles  of  both  members  fully  developed. 

INTRUSIVE  SHEET. — A  mass  of  volcanic  rock  lying  in  a  flat 
bed,  surrounded  by,  and  often  replacing,  other  rocks. 

ISOMORPHOUS. —Having  the  same  form.  Chemical  substances 
and  minerals  which  are  isomorphous  are  not  only  similar 
in  crystalline  form  but  also  in  composition,  and  molecules 
of  isomorphous  substances  are  often  found  to  replace  one 
another.  The  Felspar  group  affords  a  good  example. 

ISOTROPIC. — Substances  which  have  but  one  index  of  refraction 
of  light.  All  "cubic  crystals  and  all  colloid  substances  that 
transmit  light  are  isotropic. 

LENTICULAR. — Having  the  shape  of  a  bi-convex  lens. 


GLOSSARY.  295 

LITHOSPHERE. — The  region  of  land,  as  distinguished  from  air 

and  water. 
MAGMA. — The  rock-bulk.    Crystals  separating  from  the  Magma 

are  those  that  crystallise  out  while  the  bulk  of  the  rock  is 

in  a  fluid  or  semi-fluid  condition. 
MAMMILATED. — Having  the  rounded  form    of   the  mamma  or 

breast. 
MENISCUS. — A  solid  contained  between  two  surfaces  of  different 

curvatures,  or  between  two  such  surfaces  and  the  surface 

of  a  cylinder ;    the  former  is  thicker  in  the  centre  than  at 

the  edges,  while  the  reverse  is  the  case  in  the  latter  form. 
MILLING  CUTTER. — A  wheel  armed  with  cutting  edges  arranged 

like  the  teeth  of  a  circular  saw  and  so  mounted  that  it  can 

be  made  to  move  in  a  required  direction  while  rotating. 
MINERAL. — A    homogeneous    substance    formed    without    the 

agency  of  organic  life  ;   it  is  of  definite  composition  and 

usually  of  definite  form. 
MINERAL  VEINS.— Fault  fissures  which  have  been  filled  with 

mineral  matter,  usually  that  deposited  from  uprising  heated 

water. 
MOLECULE. — The    smallest    amount  of   a  chemical    substance 

that  can  exist  by  itself. 
MONOCHROMATIC. — Of  one  colour. 
NEWTON'S  EINGS. — Eings  of  coloured  light  seen  when  a  thin 

film  of  air,  or  other  matter,  is  left  between  two  surfaces 

separated  by  a  very  small  distance  from  one  another. 
NORMAL. — At  right  angles.     Thus,  a  plane  normal  to  an  axis  of 

a  crystal  is  so  placed  that  any  line  in  the  plane  is  at  right 

angles  to  that  axis. 
OPTICALLY   DENSER   MEDIUM. — A    substance    through    which 

light  waves  travel  with  less  rapidity  than  they  do  through 

the  standard  substance. 
OPTICALLY  EARER  MEDIUM. — A  substance  through  which  light 

waves  travel  with  greater  rapidity. 

OSMOSIS. — A  force  which   impels    a    solvent  through  a  semi- 
permeable  medium,  from  a  less  concentrated  solution  to  a 

more  concentrated. 


296  GLOSSAEY. 

PHOSPHORESCENCE. — The  emission  of  light  by  a  substance  after 
being  heated,  rubbed  or  exposed  to  light  or  other  forms  of 
radiant  energy.  So  called  from  the  marked  presence  of  the 
phenomenon  in  phosphorus. 

PLANE  OF  INCIDENCE. — The  plane  containing  an  incident  ray  of 
light  and  the  normal  to  the  surface  on  which  the  light 
falls. 

PLUTONIC  BOCKS. — Bocks  which  have  consolidated  at  great 
depths  and  hence  under  great  pressure. 

POLYSYNTHETIC  TWINNING. — Bepeated  twinning  parallel  to  one 
plane. 

PSEUDOMORPH. — Having  the  external  form  of  another  substance; 
thus,  Turquois  which  has  no  external  crystalline  form  of 
its  own  may  be  found  in  the  form  of  a  crystal  of  Felspar 
through  a  gradual  decomposition  of  the  Felspar  with 
formation  of  Turquois. 

BE-ENTERING  ANGLE. — A  hollow  angle  contained  between  two 
planes,  similar  to  the  under  surface  of  the  roof  of  a  house. 

BEFLECTION  OF  LIGHT. — The  turning  back  of  light  when  it 
strikes  a  polished  surface.  The  angles  of  incidence  and  of 
reflection  are  equal  and  in  the  same  plane. 

BEFRACTION. — The  retardation  or  acceleration  of  light  waves  on 
entering  a  more  or  less  dense  medium,  bending  the  ray. 

BEFRACTION,  SINGLE. — The  simple  bending  of  the  light  ray  that 
occurs  equally  in  all  directions  in  a  transparent  amorphous 
or  cubic  substance. 

BEFRACTION,  DOUBLE. — The  bending  of  a  light  ray  in  two 
directions  that  occurs  in  all  transparent  substances  not 
either  amorphous  or  cubic. 

BHOMBOHEDRA. — Solid  figures  contained  by  six  planes,  opposite 
pairs  of  planes  being  parallel,  and  the  three  upper  planes 
all  inclined  to  the  vertical  axis  at  equal  angles.  The  form 
may  be  conceived  by  the  extension  of  alternate  faces  of  the 
double  hexagonal  pyramid,  six  faces  instead  of  twelve 
being  present ;  were  the  other  six  faces  of  a  similar  pyramid 
developed,  the  two  forms  would  be  positive  and  negative 
rhombohedra  of  the  same  order. 


GLOSSABY.  297 

SALIENT  ANGLE. — The  outward  projecting  angle  formed  by  the 
meeting  of  two  planes. 

SHAK. — A  cavity  in  a  limestone  rock. 

SILICA. — The  dioxide  of  silicon  ;  often  used  as  a  term  to  include 
all  the  naturally  occurring  forms  of  this  oxide. 

SOLFATARA. — A  small  vent  in  the  neighbourhood  of  a  volcano, 
emitting  sulphurous  vapours. 

SOLID  ANGLE. — The  corner  formed  by  the  meeting  in  a  point  of 
three  or  more  planes. 

SPECIFIC  GRAVITY. — The  ratio  of  the  weight  of  a  substance  in 
air  to  the  weight  of  an  equal  volume  of  water  at  its 
maximum  density. 

STRASS. — The  glass  used  for  the  production  of  artificial  gems. 

SURFACE  CHARGE  OF  ELECTRICITY. — A  charge  of  electricity  on 
a  surface,  the  potential  or  electrical  tension  varying  at 
different  points  on  the  surface,  as  at  the  two  ends  of  a 
Tourmaline  crystal. 

SURFACE  TENSION. — A  force  acting  between  a  surface  and  a 
medium  with  which  it  is  in  contact.  The  total  force  in  a 
given  case  is  proportional  to  the  area  of  the  surface. 

THERMAL  SPRINGS. — Springs  of  uprising  heated  water. 

THERMO-METAMORPHISM. — A  change  induced  in  rocks  as  the 
result  of  the  action  of  heat,  and  probably  of  heated  water. 

TRACE  (OF  A  PLANE). — The  line  along  which  the  plane  cuts 
another  plane. 

TRANSLUCENT.- — Allowing  light  to  pass  ;  distinguished  from 
transparent  in  not  allowing  objects  to  be  definitely  seen. 

TRANSPARENT. — Allowing  light  to  pass  so  freely  that  definite 
images  of  the  objects  reflecting  or  emitting  the  light  are 
formed  on  the  retina. 

TRISOCTAHEDRON. — A  generally  octohedral  form  of  the  cubic 
system  in  which  each  face  of  the  octahedron  is  replaced  by 
three  planes ;  when  each  of  these  planes  has  three  angles 
the  form  is  a  trigonal  trisoctahedron ;  when  each  of  the 
planes  has  four  angles  the  form  is  a  tetragonal  trisocta- 
hedron (Fig.  24). 

UNCONFORMITY. — The  relation  between  two   rocks   when   the 


298  GLOSSARY. 

newer  has  been  deposited  on  the  eroded  surface  of  the 

older. 
UNDULATIONS  OF  LIGHT. — The  waves  in  the  ether  which  give 

rise  to  the  phenomenon  of  light. 
UNIAXIAL    CEYSTALS. — Those   having   one   direction,   and   one 

only,  in  which  light  suffers  no  double  refraction ;  crystals 

belonging  to  the  tetragonal  and   hexagonal    systems   are 

uniaxial. 
UNIT    EHOMBOHEDRON. — The    rhombohedron    which   may   be 

regarded  as  developed  from  the  extension  of  alternate  faces 

of  a  hexagonal  pyramid,  each  face  of  which  pyramid  would 

cut  the  vertical  axis  at  unit  length  and  two  of  the  horizontal 

axes  at  unit  length. 
VACUUM  TUBE. — A  closed  tube  which  contains  two  electrical 

terminals  and  which  has  been  exhausted  to  a  high  degree  ; 

on  passing  a  current  of  electricity  of  high  potential  through 

the  tube,  emanations,  whose  properties  differ  widely  from 

ordinary  light  waves,  are  produced. 
VIBRATIONS  OF  LIGHT. — See  "  Undulations." 
ZEOLITE. — A  Zeolite  may  be  regarded  as  a  mineral  consisting  of 

hydrous  non-magnesian  silicates,  of  epigene  origin,  which 

froths  up  before  the  blow-pipe. 


INDEX. 


ABRASIVES,  60,  61,  63 
Absorption  Spectra,  32 

in  Garnet,  249 
in  Zircon,  260 
Achates,  166 
Achroite,  277 
Adamantine  Spar,  185 
Adamas  Siderites,  185 
Adelaide  Ruby,  249 
Adularescence,  31 
Adularia,  210 
Agate,  165 

applications,  170 

Brecciated,  174 

cutting  of,  173 

Eyed,  13 

Faulted,  168 

Fortification,  13 

Mocha,  14 

Moss,  12 

origin  of,  11 

priming  of,  12 

Ribbon,  174 

shape  of,  14 

skin  of,  13,  167 

staining,  171 

tube  of  escape,  14 

Vein,  14,  174 


t  gate-opal,  181 
kerite,  200 
Alabandin  Ruby,  198 
Alabaster,  286 

Egyptian,  207 
Alabastrites,  207 
Alalite,  219 
Albite,  214 

labradorescent,  214 
Albite-moonstone,  214 
Alexandrite,  201 
Allotriomorphic  crystals,  49 
Allotriomorphism,  19 
Almandine,  248 

Spinel,  198 
Aluminium  pencil  test  for  gems, 

70 

Amazonstone,  213 
Amber,  287 
Ambre  Antique,  289 
Amethyst,  152 

Oriental,  196 
Purple,  196 
Amphibole,  223 
Andalusite,  268 
Andradite,  249 
Angle,  critical,  25 

of  incidence,  23 
of  refraction,  23 
Anisotropic  minerals,  28 


300 


INDEX. 


Apatite,  283 
Aphrizite,  276 
Aquamarine,  229 

Chrysolite,  229 
Arizona  Ruby,  248 
Artificial  gem  production,  pioneers 

of,  78 

precious  stones,  70 
Asteria,  183 
Asteriated  Cordierite,  240 

Corundum,  196 

Quartz,  152 

Ruby,  190 

Sapphire,  195 
Asterism,  31 

in  Garnet,  244 
Attachment  of  crystals,  49 
Augite,  218 
Authorities,  early,  2 
Aventurine  Oligoelase,  215 
Orthoclase,  212 
Quartz,  159 
Axe  Stone,  224 
Axes  of  crystals,  47 
Axinite,  272 
Azure  Stone,  240 

B. 

BALAS  Ruby,  198 
Banded  Agate,  168 
Birkenfeld,  Agate  industry  of,  65 
Beryl,  228 
Beryllus,  228,  253 
Bezils,  53 

Bishop's  Stone,  153 
Black  Garnet,  249 
Bleached  Agate,  169 
'Bloodstone,  165 
Blue  ground,  108 
Blue  John,  144 
Bohemian  Garnet,  246 
Ruby,  155 


Bort,  94,  103 

applications  of,  131 
Bottle  stone,  254 
Brazilian  Diamond  localities,  113 

Emerald,  277 

Pebble,  150 

Ruby,  266 

Sapphire,  266,  276 

Topaz,  266 

Brecciated  Agate,  174 
Brilliant  cut,  51,  53 
Briolette,  55 
Bristol  'Diamonds,  150 
Brittleness  of  gems,  41 
Brutage,  57 
Burning,  76,  263 
Burnt  T.opaz,  264 
Burton's  preparation  of  Diamond, 
87 

C. 

CACHALONG,  13,  166 

Opal,  181 
Cairngorm,  156 
Calcedonius  (Dioptase),  161 
Calcite,  205 

origin  of,  11 
Callais  (of  Pliny),  284 
Callina  (of    Pliny).     See  Olrvine, 

253 

Cameos,  detection  of  artificial,  69 
Cape  Chrysolite,  274 

Ruby,  247 
Carbonado,  103,  117 

applications  of,  131 
Carborundum,  63 
Carbunculus,  198,  243 

Alabandicus,  248 
Carnelian,  162 

origin  of,  14 
Agate,  169 
Cat  Sapphire,  184 


INDEX. 


801 


Cat's  Eye,  201 

Ceylon,  203 

Occidental,  158 

Oriental,  203 

Quartz,  158 
Ceylonese  Cat's  Eye,  203 

Chrysolite,  277 

Opal,  211 

Peridot,  277 

Euby,  249 
Ceylonite,  199 
Chalcedony,  161 

origin  of,  11 
Change  of  colour,  31 
Charles  the  Bold's  Diamond,  50 
Chatoyency,  31 
Chiastolite,  268 
Chloromelanite,  223 
Chlorospmel,  198 
Chrysoberyl,  201 

of  the  ancients  : — 
See  Chrysoprase,  163 
See  Chrysolite,  253 
Chrysoberyllus,  229 
Chrysocolla  of  Theophrastus,  208 
Chrysolite,  253 

Aquamarine,  229 
Cape,  274 

Ceylonese,  277 

Oriental,  196 

Saxon,  267 

Chrysolithus.     See  Topaz,  262 
Chrysoprase,  163 
Chrysoprasius,  163,  229 
Cinnamonstone,  245 
Citrine,  155 
Cleavage,  44 
Cloud  Agate,  169 
Colorado  Ruby,  248 
Colour  of  minerals,  21 
Common  Garnet,  248,  249 
Copper  Emerald,  255 


Corallachates,  159 
Cordierite,  238 

Asteriated,  240 
Corundum,  183 

Common,  185,  196 
Crocidolite,  226 

Crookes    on   production   of    Dia- 
monds, 85 

Crown  (of  cut  gems),  53 
Crystal  cups,  146 
Crystal  models,  construction  of, 

48 

Crystalline  form,  46 
Crystallisation,    Boyle's    descrip- 
tion of,  15 

Crystallographic  faces,  46 
forms,  46 
systems,  47 
Crystallus,  146 

Crystals,  modes  of  formation  of,  7 
Culasse  (of  cut  gems),  53 
Cutting  en  cabochon,  56 
pressure  for,  61 
speed  of,  60 
Cyanite,  269 
Cymophane,  201 

D. 

DEMANTOID,  249 

Dense  solutions,  36 

Detection  of  imitation  gems,  70, 

74 
Diamond,  93 

a  reputed  poison,  6 
anomalous    double  re- 
fraction, 96 
applications  of,  131 
artificial,  extraction  of, 

84 

production, 
81 


302 


INDEX. 


Diamond,    associated    minerals, 

122 
Australian      localities, 

118 

Bristol,  150 
chemical  composition, 

127 

cleavage,  98 
cleaving,  57 
colour,  94 
constitution  of,  80 
counterfeiting,  185 
crystalline  form,  99 
dispersion  of,  96 
early  record  of,  93 
effect  of  X-rays  on,  97 
electrical      behaviour, 

97 
European       localities, 

119 

famous  specimens,  136 
glaziers,  131 
"grain"  of,  62 
grinding,  60 
hardness,  98 
inclusions  in.  102 
Lake  George,  150 
localities,  105 
lustre  of,  95 
Matura,  261 
mining,  128 
North  American  locali- 
ties, 120 

origin  of,  80,  104,  124 
phosphorescence  of,  96 
plateau  deposits,  115 
Pliny's  description  of, 

93 

polishing,  60 
recognition  of,  136 
refraction  of,  95 
"  ripe,"  94 


Diamond  river  deposits,  114 

setting  of,  134 

slitting  of,  58 

South    African     locali- 
ties, 105 

temperature     of     igni- 
tion, 97 

"  unripe,"  94 

valley  deposits,  115 

value  of,  134 
Diaphaneity,  23 
Dichroite,  238 
Dichroscope,  30 
Dioptas.e,  255 

origin  of,  11,  15 
Diopside,  218 
Dispersion  of  light,  24 
Dop,  59 
Doublets,  77 

Doubly  Refracting  Spar,  205 
Dravite,  277 

Dresden  Green  Diamond,  94 
Dynamo-metamorphism,  19 

E. 

EGYPTIAN  Emerald  mines,  232 

Jasper,  175 
Eisenkiesel,  160 
Electrical  phenomena  of  minerals, 

34 

Electrum,  287 
Elie  Euby,  247 
Emerald,  229 

artificial,  91 

Brazilian,  277 

Copper,  255 

False,  131 

mossy,  237 

Oriental,  196 

Uralian,  250 

value,  237 
Emery,  185,  197 


INDEX. 


303 


Engraved  pastes,  68 
Epidote,  271 
Essence  d'Orient,  75 
Essonite,  245 
Euclase,  270 
Eyed  Agate,  169 


F. 

FACE,  crystal,  46 
Fallow  Topaz,  267 
False  Emerald,  131 

Sapphire,  145 

Topaz,  131 
Fell,  the  strass  of,  71 
Felspar,  209 
Feminine  Lazurite,  241 
Euby,  184 
Sapphire,  184 
Fire  Marble,  207 

Opal,  180 
Flame  Opal,  178 
Flaws,  effect  of,  54,  75 
Fleclies  d'amour,  157 
Flies  in  Amber,  288 
Flint,  174 

Fluorescence,  31,  142 
Fluor  Spar,  141 
Form,  crystal,  46 
Formation  of  gems,  early  theories, 

7 

Fortification  Agate,  169 
Fracture,  41 
Fusibility,  34 


G. 

GARNET,  243 

Adelaide  Kuby,  249 
Almandine,  248 
Andradite,  249 


Garnet,  Arizona  Ruby,  248 
Black,  249 
Bohemian,  246 
Cape  Ruby,  247 
Ceylonese  Ruby,  249 
Colorado  Ruby,  248 
Common,  248,  249 
Demantoid,  249 
Elie  Ruby,  247 
Hessonite,  245 
Oriental,  248 
Precious,  246,  248 
Pyrope,  246 
Rhodolite,  250 
Rock  Ruby,  246 
"  shells,"  251 
Spessartite,  249 
"  Syrian,"  249 
Topazolite,  250 
Uvarovite,  250 
Vermeille,  246,  248 

Gems,  early  use  of,  1 

Gem-cutting,  early,  50 

Genesis  of  precious  stones,  9 

Gibraltar  Stone,  207 

Girasol,  180, 181 

(Adularia),  211 
Opal,  180 

Girdle,  53 

Glass  for  imitation  gems,  71,  73 

Golconda  Diamond  mines,  111 

Gold  Opal,  178 

Golden  Beryl,  229 

Gooseberry  Stone,  246 

Goutte  d'e  Suif,  56 

Gouttes  d'Eau,  267 

Granite,  gems  in,  19 

Grenat,  243 

See  also  Zircon,  259 

Gurgulho,  115 

Gypsum,  286 

origin  of,  10,  15 


304 


INDEX. 


H. 

HALF-BRILLIANT,  55 

Hardness,  42 

table  of,  44 

Harlequin  Opal,  178 

Haiiyne,  240 

Hawk's  Eye,  226 

Heat,  conductivity  of,  38 
effects  of,  33 

Heliolite,  215 

Heliotrope,  165 

of  Pliny,  164 

Hessonite,  245 

Hiddenite,  220 

Hope  Blue  Diamond,  95 

Hornblende,  224 

Hornstone,  174 

Hyacinth,  261 

of  Compostella,  160 
Oriental,  196 

Hyacinthus,  183 

Hyalite,  182 

Hydrophane,  181 

Hydrostatic  balance,  39 


IASPIS,  161,  164 

Idiornorphic  crystals,  49 

Idiomorphism,  19 

Idocrase,  256 

Indian  Topaz,  266 

Indicolite,  276 

Indigolite,  276 

Inscription,  supposed  effect  of,  3 

Intercepts,  crystal,  47 

Intrusive  rock,  origin  of,  17 

lolite,  238 

Iridescence,  31 

Iris  Quartz,  152 

Itacolumite,  114 


J. 

JADE  (Jadeite),  222 

(Nephrite),  224 
Jadeite,  224 
Jargon,  261 
Jasp-opal,  182 
Jasper,  174 

Agate,  169 

Egyptian,  175 

origin  of,  15 

Wood,  175 
Jet,  289 

K. 

KIDNEY  Stone,  224 
Kimberley  Diamond  mines,  107 
Koh-i-Noor,  cutting  the,  61 
Kunzite,  220 
Kyanite,  269 


LABRADORESCENCE,  31 

Labradorite,  215 

Lap  for  Diamonds,  60 
for  softer  gems,  63 

Lapis  Lazuli,  240 
Lyncurius,  4 
Tiburtinus,  208 

Lazurite,  240 

Lechosos  Opal,  180 

Leucachates,  161 

Leuco-sapphire,  184 

Ligure,  259 

Loss  of  weight  in  cutting,  66 

Louis  de  Berquem,  50 

Lumacello,  207 

Lustre  of  minerals,  22 

Lychnis,  183,  198 

Lydian  Stone,  174 

origin  of,  17 


INDEX. 


305 


Lygdinus,  286 
Lyncurium,  259 

(Amber),  288 
Lynx- sapphire,  184,  240 

M. 

MAGICAL  properties,  5 
Magnetic  phenomena,  35 
Malachite,  208 
Malacolite,  219 
Masculine  Lazurite,  241 

Euby,  184 

Matura  Diamond,  261 
Menilite,  181 
Microcline,  213 
Milk  Opal,  181 
Milky  Quartz,  157 
Mocha,  167,  169 
Mobs'  scale  of  hardness,  42 
Moissan's  artificial  Diamonds,  82 
Montana  Sapphires,  193 
Moonstone,  Albite,  214 

,,          Orthoclase,  211 
Morion,  156 
Mormorion,  156 
Moss  Agate,  169 
Mother  of  Opal,  179 
Muller's  Glass,  182 
Murrhine  vases,  146 
Mushrooms,    supposed    germina- 
tion of,  4 
Mussite,  219 

N. 

NEEDLE  Stone,  157 
Nephrite,  224 
Nero's  eye  glass,  219 
Nicol's  prism,  29 
Noble  Chrysolite,  254 
Serpentine,  281 
P.S. 


0. 


OCCIDENTAL  Amethyst,  153 
Cat's  Eye,  158 
Topaz,  155 
Oligoclase,  214 
Olivine,  253 
Onyx,  168,  172 

Agate,  168 
Mexican,  207 
of  Pliny,  207 
origin  of,  13 
Opal,  176 

Agate,  181 
Cachalong,  181 
Ceylonese  (Adularia),  211 
Common,  181 
Fire,  180 
Flame,  178 
Girasol,  180 
Gold,  178 
Harlequin,  178 
Lechosos,  180 
Milk,  181 
origin  of,  11 
Pin  Point,  178 
Precious,  178 
Kesin,  181 
Sun,  180 

Water  (Adularia),  211 
Wood,  182 
Opalescence,  31,  177 
Ophthalmius,  176 
Optic  axes,  27 

Oriental  Amethyst,  183,  196 
Chrysolite,  184,  196 
Emerald,  184,  196 
Garnet,  248 
Hyacinth,  184,  196 
Topaz,  183,  196 
Turquois,  286 


306 


INDEX. 


Orthoclase,  210 

labradorescent,  212 
Sunstone,  212 

P. 

PASTES,  cutting,  74 

Egyptian,  67 
engraved,  68 
production  of,  68 

Pavilions,  53 

Pearls,  artificial,  75 

Pechopal,  181 

Peridot,  254 

Ceylonese,  277 

Peristerite,  214 

Peruvian  Emerald,  233 

Phenakite,  254 

Phosphorescence,  30 

Picotite,  198 

Pin  Point  Opal,  178 

Pinking,  263 

Pipes,  volcanic,  109 

Pitt  Diamond,  54 

Plasma,  164 

Pleochroism,  30 

Pleonaste,  198 

Point  cut,  51,  55 

Polarisation  of  light,  28 

Polishing,  64 

dangers  of,  65 

Prase,  164 

Precious  Amethyst,  153 
Beryl,  229 
Garnet,  246,  248 
Opal,  177 
Serpentine,  281 

Prehnite,  273 

origin  of,  11 

Prime  d' Amethyst,  155 

Prince  Rupert's  drops,  96 

Pyroelectricity,  34 

Pyrope,  246 


Q. 
QUARTZ,  146 

applications  of,  150 
Asteriated,  152 
Aventurine,  159 
Cat's  Eye,  158 
containing     other     sub- 
stances, 160 
Iridescent,  152 
Iris,  152 
Milky,  157 
*  origin  of,  11 
Eainbow,  152 
Rose,  155 
Sagenitic,  157 
Sapphire,  157 
Smoky,  156 
staining  of,  151 
Star,  152 
Yellow,  155 


R. 

RAINBOW  Quartz,  152 
Refraction,  double,  27 
index  of,  24 
measurement  of,  26 
single,  23 

Refractive  indices,  table  of,  32 
Refractometer,  26 
Resin  Opal,  181 
Rhodolite,  250 
Ribbon  Agate,  168,  174 
Ring  Agate,  168 
Rock  Crystal,  149 

drills,  131 

Ruby,  246 
Rontgen  rays,  32 
Rose  cut,  51,  55 

Quartz,  155 
Rosette,  55 
Rubellite,  276 


INDEX. 


307 


Rubicelle,  198 

Ruby.     See  Corundum,  183 

Adelaide,  249 

Alabandin,  198 

Arizona,  248 

artificially  produced,  88 

Asteriated,  190 

Balas,  191,  198 

Bohemian,  155,  192 

Brazilian,  192,  266 

Cape,  247 

Ceylonese,  249 

Colorado,  248 

Elie,  191,  247 

False,  141,  192 

Feminine,  184 

Geneva,  88 

localities  for,  188 

Masculine,  184 

Rock,  191,  246 

Spinel,  198 

True,  188 

S. 

SAGENITIC  Quartz,  157 

Sandaster,  159 

Saphir  d'Eau,  194,  239 

tiappare,  269 

Sapphire.     See  Corundum,  183 

artificially    produced, 

89 

Asteriated,  195 
Brazilian,  266,  276 
Cat,  184 
False,  145 
Leuco,  184,  195 
localities  for,  192 
Lynx,  184,  240 
Montana,  193 
of  de  Saussure,  194 
Quartz,  157 
Spinel,  198 


Sapphire,  Star,  198 

Water,  184,  239 
Sapphirus,  240 
Sard,  163 
Sardius,  162 
Satin  Spar  (Calcite),  206 

(Gypsum),  286 
Saxon  Chrysolite,  267 

Topaz,  267 
Schorl,  276 
Sequence  of  mineral  deposition, 

18 
Serpentine,  280 

origin  of,  11 
Siberian  Topaz,  266 
Siberite,  276 
Siderite  (Quartz),  157 
Siliceous  Sinter,  174 
Sinople,  160 

Sinter,  Siliceous,  174,  182 
Skief,  60 
Skill- facets,  53 
Slitting  Diamonds,  58 

softer  gems,  65 
Smaragdus,  228 

(Olivine),  253 
(Turquois),  284 
Medicus,  208 
Smoky  Quartz,  156 
Sodalite,  240 
Solder  for  dops,  59 
Solubility,  effect  of  great  heat  on, 

8 
Spanish  Emerald,  233 

Topaz,  155 
Specific  gravity,  35 

bottle,  36 
determination 

of,  36 

solutions,  36 
table  of,  40 
Spessartite,  249 


308 


INDEX. 


Sphene,  281 
Spiller  Amber,  289 
Spinel,  198 

Almandme,  198 
Kuby,  198 
Sapphire,  198 
Spodumene,  220 
Staining  precious  stones,  76 
Stalactitic  Agate,  168 
Star  facets,  53 

Quartz,  152 

Sapphire,  195 
Staurolite,  279 
Step  cut,  55 
Strass,  68,  72 
Succinite,  288 
Succinum,  288 
Sun  Opal,  180 
Sunstone  (Oligoclase),  214 
(Orthoclase),  212 
Syrian  Garnet,  249 

T. 

TABLE  cut,  51,  55 

Tables  of  the  Law,  240 

Tallow  Drops,  56 

Tassie,  James,  68 

Tauridan  Topaz,  266 

Thermo -metamorphic    products, 

18 

Thetis'  Hair  Stone,  158 
Tiger's  Eye,  226 
Topaz,  262 

Brazilian,  266 

Burnt,  76 

Fallow,  267 

False,  131 

Indian,  266 

Occidental,  155 

Oriental,  196 

Saxon,  267 

Spanish,  155 


Topazios  (Topazius),  253,  262 
Topazolite,  250 
Total  internal  reflection,  25 
Touchstone,  174 
Tourmaline,  274 

Achroite,  277 
Aphrizite,  276 
(Brazilian  Emerald), 

277 
'(Brazilian  Sapphire), 

276 

(Ceylonese     Chryso- 
lite), 277 
(Ceylonese   Peridot), 

277 

deformation  of,  20 
Dravite,  277 
Indicolite,  276 
plates,  278 
Kubellite,  276 
Schorl,  276 
Siberite,  276 
Travertine,  208 
Triplets,  77 
Turquois,  284 

artificial,  91 
origin  of,  11,  15 

U. 

ULTRAMARINE  pigment,  243 
Uralian  Emerald,  250 
Uvarovite,  250 

V. 

VARNISHING  inferior  gems,  77 
Vein  Agate,  174 
Venus'  Hair  Stone,  157 
Vermeille,  246,  248 

Oriental,  196 

Verneuil,  artificial  Euby,  90 
Vesuvian,  256 


INDEX. 


309 


W. 

WATER  Opal,  211 

Sapphire,  239 
Wolf's  Eye,  211 
Wollaston,  57 
Wood  Jasper,  175 
Opal,  182 

X. 

X-BAYS,  effect  of,  on  Diamond,  97 


X-rays,  effect  of,  on  Kunzite,  220 
Xanthite,  257 

Y. 

Yu  (Yu-shih),  223,  224 

Z. 


ZIRCON,  259 


artificial,  91 


BIIADBUKY,    AGNEW,    &   CO.   LD.,    POINTERS,   LONDON   AND   TONBK1DGE. 


P.S. 


VAN     NOSTRAND'S 

"Westminster    Series 

Bound  in  uniform  style.   Fully  Illustrated.   Price  $2-00  net  each. 


The  Volumes  in  the  "  Westminster"  Series  have 
been  designed  to  meet  the  growing  demand  for  books 
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THE    "WESTMINSTER"    SERIES 

CoaL  By  JAMES  TONGE,  M.I.M.E.,  F.G.S.,  etc.  (Lecturer 
on  Mining  at  Victoria  University,  Manchester).  With 
46  Illustrations,  many  of  them  showing  the  Fossils  found 
in  the  Coal  Measures. 

LIST  OF  CONTENTS  :  History.  Occurrence.  Mode  of  Formation 
of  Coal  Seams.  Fossils  of  the  Coal  Measures.  Botany  of  the 
Coal-Measure  Plants.  Coalfields  of  the  British  Isles.  Foreign 
Coalfields.  The  Classification  of  Coals.  The  Valuation  of  Coal. 
Foreign  Coals  and  their  Values.  Uses  of  Coal.  The  Production 
of  Heat  from  Coal.  Waste  of  Coal.  The  Preparation  of  Coal 
for  the  Market.  Coaling  Stations  of  the  World.  Index. 

This  book  on  a  momentous  subject  is  provided  for  the  general 
reader  who  wishes  accurate  knowledge  of  Coal,  its  origin,  position 
and  extent,  and  its  economical  utilization  and  application. 

Iron  and  Steel.    By  J.  H.  STANSBIE,  B.Sc.  (Lond.),  F.I.C. 

With  86  Illustrations. 

LIST  OF  CONTENTS  :  Introductory.  Iron  Ores.  Combustible  and 
other  materials  used  in  Iron  and  Steel  Manufacture.  Primitive 
Methods  of  Iron  and  Steel  Production.  Pig  Iron  and  its  Manu- 
facture. The  Refining  of  Pig  Iron  in  Small  Charges.  Crucible 
and  Weld  Steel.  The  Bessemer  Process.  The  Open  Hearth 
Process.  Mechanical  Treatment  of  Iron  and  Steel.  Physical 
and  Mechanical  Properties  of  Iron  and  Steel.  Iron  and  Steel 
under  the  Microscope.  Heat  Treatment  of  Iron  and  Steel.  Elec- 
tric Smelting.  Special  Steels.  Index. 

The  aim  of  this  book  is  to  give  a  comprehensive  view  of  the  modern 
aspects  of  iron  and  steel,  together  with  a  sufficient  account  of  its  his- 
tory to  enable  the  reader  to  follow  its  march  of  progress.  The  methods 
of  producing  varieties  of  the  metal  suitable  to  the  requirements  of 
the  engineer,  foundryman  and  mechanician  are  described  so  that  the 
worker  may  learn  the  history  of  the  material  he  is  handling. 

Natural  Sources  of  Power,    By  ROBERT  S.  BALL,  B.Sc., 

A.M.Inst.C.E.  With  104  Diagrams  and  Illustrations. 
CONTENTS  :  Preface.  Units  with  Metric  Equivalents  and  Abbre- 
viations. Length  and  Distance.  Surface  and  Area.  Volumes. 
Weights  or  Measures.  Pressures.  Linear  Velocities,  Angular 
Velocities.  Acceleration.  Energy.  Power.  Introductory 
Water  Power  and  Methods  of  Measuring.  Application  of  Water 
Power  to  the  Propulsion  of  Machinery.  The  Hydraulic  Turbine. 
Various  Types  of  Turbine.  Construction  of  Water  Power  Plants. 
Water  Power  Installations.  The  Regulation  of  Turbines.  Wind 
Pressure,  Velocity,  and  Methods  of  Measuring.  The  Application 
of  Wind  Power  to  Industry.  The  Modern  Windmill.  Con- 
structional Details.  Power  of  Modern  Windmills.  Appendices 
A,  B,  C.  Index. 
Two  departments  of  Engineering  and  their  applications  to  industry 

form  the  subject  of  this  volume  :    the   "  natural  "  sources  of  water 

(    2    ) 


THE     '  WESTMINSTER  "    SERIES 

and  wind  power  which  supply  mechanical  energy  without  any  inter- 
mediate stage  of  transformation.  Most  people  will  be  surprised  at 
the  extent  to  which  these  natural  power  producers  are  used.  The 
widespread  application  of  water  power  is  generally  known,  but  it  is 
interesting  to  learn  that  the  demand  for  windmills  was  never  so  great 
as  it  is  to-day,  and  there  are  signs  of  abnormal  expansion  in  the  direc- 
tion of  their  useful  application  in  the  great  agricultural  countries  of 
the  world.  Though  primarily  of  importance  to  the  engineer,  this  work 
will  be  of  great  interest  to  every  manufacturer  who  in  economizing 
his  means  of  power  production  can  take  the  natural  forces  that  lie 
to  his  hand  and  harness  them  in  his  service.  The  author  is  the  son 
of  Sir  Robert  Ball,  the  eminent  mathematician  and  astronomer. 

Liquid  and  Gaseous  Fuels,  and  the  Part  they  play 
in  Modern  Power  Production.  By  Professor 
VIVIAN  B.  LEWES,  F.I.C.,  F.C.S.,  Prof,  of  Chemistry, 
Royal  Naval  College,  Greenwich.  With  54  Illustrations. 

LIST  OF  CONTENTS  :  Lavoisier's  Discovery  of  the  Nature  of  Com- 
bustion, etc.  The  Cycle  of  Animal  and  Vegetable  Life.  Method 
of  determining  Calorific  Value.  The  Discovery  of  Petroleum 
in  America.  Oil  Lamps,  etc.  The  History  of  Coal  Gas.  Calorific 
Value  of  Coal  Gas  and  its  Constituents.  The  History  of  Water 
Gas.  Incomplete  Combustion.  Comparison  of  the  Thermal 
Values  of  our  Fuels,  etc.  Appendix.  Bibliography.  Index. 

The  subject  of  this  book  has,  during  the  last  decade,  assumed  such 
importance  that  it  is  hoped  this  account  of  the  history  and  develop- 
ment of  the  use  of  various  forms  of  combustible  liquids  and  gases 
for  the  generation  of  energy  may  do  some  service  in  its  advancement. 

Electric  Power  and  Traction.  By  F.  H.  DAVIES, 
A.M.I. E.E.  With  66  Illustrations. 

LIST  OF  CONTENTS  :  Introduction.  The  Generation  and  Distri- 
bution of  Power.  The  Electric  Motor.  The  Application  of 
Electric  Power.  Electric  Power  in  Collieries.  Electric  Power 
in  Engineering  Workshops.  Electric  Power  in  Textile  Factories. 
Electric  Power  in  the  Printing  Trade.  Electric  Power  at  Sea. 
Electric  Power  on  Canals.  Electric  Traction.  The  Overhead 
System  and  Track  Work.  The  Conduit  System.  The  Surface 
Contact  System.  Car  Building  and  Equipment.  Electric  Kail- 
ways.  Glossary.  Index. 

The  majority  of  the  allied  trades  that  cluster  round  the  business  of 
electrical  engineering  are  connected  in  some  way  or  other  with  its  power 
and  traction  branches.  To  members  of  such  trades  and  callings,  to 
whom  some  knowledge  of  applied  electrical,  engineering  is  desirable 
if  not  strictly  essential,  the  book  is  particularly  intended  to  appeal. 
It  deals  almost  entirely  with  practical  matters,  and  enters  to  some 
extent  into  those  commercial  considerations  which  in  the  long  run 
must  overrule  all  others. 

(  3  ) 


THE    "WESTMINSTER"    SERIES 


Town  Gas  and  its  Uses  for  the  Production  of 
Light,  Heat,  and  Motive  Power.  By  W.  H.  Y. 
WEBBER,  C.E.  With  71  Illustrations. 

LIST  OF  CONTENTS  :  The  Nature  and  Properties  of  Town  Gas.  The 
History  and  Manufacture  of  Town  Gas.  The  Bye-Products  of 
Coal  Gas  Manufacture.  Gas  Lights  and  Lighting.  Practical 
Gas  Lighting.  The  Cost  of  Gas  Lighting.  Heating  and  Warm- 
ing by  Gas.  Cooking  by  Gas.  The  Healthfulness  and  Safety 
of  Gas  in  all  its  uses.  Town  Gas  for  Power  Generation,  including 
Private  Electricity  Supply.  The  Legal  Relations  of  Gas  Sup- 
pliers, Consumers,  and  the  Public.  Index. 

The  "  country,"  as  opposed  to  the  "  town,"  has  been  defined  as 
"  the  parts  beyond  the  gas  lamps."  This  book  provides  accurate 
knowledge  regarding  the  manufacture  and  supply  of  town  gas  and  its 
uses  for  domestic  and  industrial  purposes.  Few  people  realize  the 
extent  to  which  this  great  industry  can  be  utilized.  The  author  has 
produced  a  volume  which  will  instruct  and  interest  the  generally  well 
informed  but  not  technically  instructed  reader. 

Electro-Metallurgy.  By  J.  B.  C.  KERSHAW,  F.I.C.  With 
6 1  Illustrations. 

CONTENTS  :  Introduction  and  Historical  Survey.  Aluminium. 
Production.  Details  of  Processes  and  Works.  Costs.  Utiliza- 
tion. Future  of  the  Metal.  Bullion  and  Gold.  Silver  Refining 
Process.  Gold  Refining  Processes.  Gold  Extraction  Processes. 
Calcium  Carbide  and  Acetylene  Gas.  The  Carbide  Furnace  and 
Process.  Production.  Utilization.  Carborundum.  Details  of 
Manufacture.  Properties  and  Uses.  Copper.  Copper  Refin- 
ing. Descriptions  of  Refineries.  Costs.  Properties  and  Utiliza- 
tion. The  Elmore  and  similar  Processes.  Electrolytic  Extrac- 
tion Processes.  Electro-Metallurgical  Concentration  Processes. 
Ferro-alloys.  Descriptions  of  Works.  Utilization.  Glass  and 
Quartz  Glass.  Graphite.  Details  of  Process.  Utilization.  Iron 
and  Steel.  Descriptions  of  Furnaces  and  Processes.  Yields  and 
Costs.  Comparative  Costs.  Lead.  The  Salom  Process.  The  Betts 
Refining  Process.  The  Betts  Reduction  Process.  White  Lead  Pro- 
cesses. Miscellaneous  Products.  Calcium.  Carbon  Bisulphide. 
Carbon  Tetra-Chloride.  Diamantine.  Magnesium.  Phosphorus. 
Silicon  and  its  Compounds.  Nickel.  Wet  Processes.  Dry 
Processes.  Sodium.  Descriptions  of  Cells  and  Processes.  Tin. 
Alkaline  Processes  for  Tin  Stripping.  Acid  Processes  for  Tin 
Stripping.  Salt  Processes  for  Tin  Stripping.  Zinc.  Wet  Pro- 
cesses. Dry  Processes.  Electro-Thermal  Processes.  Electro- 
Galvanizing.  Glossary.  Name  Index. 

The  subject  of  this  volume,  the  branch  of  metallurgy  which  deals 
with  the  extraction  and  refining  of  metals  by  aid  of  electricity,  is 
becoming  of  great  importance.  The  author  gives  a  brief  and  clear 
account  of  the  industrial  developments  of  electro-metallurgy,  in  lan- 
guage that  can  be  understood  by  those  whose  acquaintance  with  either 

(  4  ) 


THE    "WESTMINSTER"    SERIES 


chemical  or  electrical  science  may  be  but  slight.  It  is  a  thoroughly 
practical  work  descriptive  of  apparatus  and  processes,  and  commends 
itself  to  all  practical  men  engaged  in  metallurgical  operations,  as  well 
as  to  business  men,  financiers,  and  investors. 

Radio-Telegraphy,  By  C.  C.  F.  MONCKTON,  M.I.E.E. 
With  173  Diagrams  and  Illustrations. 

CONTENTS  :  Preface.  Electric  Phenomena.  Electric  Vibrations. 
Electro-Magnetic  Waves.  Modified  Hertz  Waves  used  in  Radio- 
Telegraphy.  Apparatus  used  for  Charging  the  Oscillator.  The 
Electric  Oscillator  :  Methods  of  Arrangement,  Practical  Details. 
The  Receiver  :  Methods  of  Arrangement,  The  Detecting  Ap- 
paratus, and  other  details.  Measurements  in  Radio-Telegraphy. 
The  Experimental  Station  at  Elmers  End  :  Lodge-Muirhead 
System.  Radio  -  Telegraph  Station  at  Nauen  :  Telefunken 
System.  Station  at  Lyiigby  :  Poulsen  System.  The  Lodge- 
Muirhead  System,  the  Marconi  System,  Telefunken  System,  and 
Poulsen  System.  Portable  Stations.  Radio-Telephony.  Ap- 
pendices :  The  Morse  Alphabet.  Electrical  Units  used  in  this 
Book.  International  Control  of  Radio-Telegraphy.  Index. 

The  startling  discovery  twelve  years  ago  of  what  is  popularly  known 
as  Wireless  Telegraphy  has  received  many  no  less  startling  additions 
since  then.  The  official  name  now  given  to  this  branch  of  electrical 
practice  is  Radio-Telegraphy.  The  subject  has  now  reached  a  thor- 
oughly practicable  stage,  and  this  book  presents  it  in  clear,  concise 
form.  The  various  services  for  which  Radio-Telegraphy  is  or  may 
be  used  are  indicated  by  the  author.  Every  stage  of  the  subject  is 
illustrated  by  diagrams  or  photographs  of  apparatus,  so  that,  while 
an  elementary  knowledge  of  electricity  is  presupposed,  the  bearings 
of  the  subject  can  be  grasped  by  every  reader.  No  subject  is  fraught 
with  so  many  possibilities  of  development  for  the  future  relationships 
of  the  peoples  of  the  world. 

India-Rubber  and  its  Manufacture,  with  Chapters 
on  Gutta-Percha  and  Batata.  By  H.  L.  TERRY, 
F.I.C.,  Assoc.Inst.M.M.  With  Illustrations. 

LIST  OF  CONTENTS  :  Preface.  Introduction  :  Historical  and 
General.  Raw  Rubber.  Botanical  Origin.  Tapping  the  Trees. 
Coagulation.  Principal  Raw  Rubbers  of  Commerce.  Pseudo- 
Rubbers.  Congo  Rubber.  General  Considerations.  Chemical 
and  Physical  Properties.  Vulcanization.  India-rubber  Planta- 
tions. India-rubber  Substitutes.  Reclaimed  Rubber.  Washing 
and  Drying  of  Raw  Rubber.  Compounding  of  Rubber.  Rubber 
Solvents  and  their  Recovery.  Rubber  Solution.  Fine  Cut  Sheet 
and  Articles  made  therefrom.  Elastic  Thread.  Mechanical 
Rubber  Goods.  Sundry  Rubber  Articles.  India-rubber  Proofed 
Textures.  Tyres.  India-rubber  Boots  and  Shoes.  Rubber  for 
Insulated  Wires.  Vulcanite  Contracts  for  India-rubber  Goods. 


THE    "WESTMINSTER"    SERIES 


The  Testing  of  Rubber  Goods.     Gutta-Percha.     Balata.     Biblio- 
graphy.    Index. 

Tells  all  about  a  material  which  has  grown  immensely  in  com- 
mercial importance  in  recent  years.  It  has  been  expressly  written 
for  the  general  reader  and  for  the  technologist  in  other  branches  of 
industry. 

Glass  Manufacture*  By  WALTER  ROSENHAIN,  Superin- 
tendent of  the  Department  of  Metallurgy  in  the  National 
Physical  Laboratory,  late  Scientific  Adviser  in  the  Glass 
Works  of  Messrs.  Chance  Bros,  and  Co.  With  Illustra- 
tions. 

CONTENTS  :  Preface.  Definitions.  Physical  and  Chemical  Qualities. 
Mechanical,  Thermal,  and  Electrical  Properties.  Transparency 
and  Colour.  Raw  materials  of  manufacture.  Crucibles  and 
Furnaces  for  Fusion.  Process  of  Fusion.  Processes  used  in 
Working  of  Glass.  Bottle.  Blown  and  Pressed.  Rolled  or 
Plate.  Sheet  and  Crown.  Coloured.  Optical  Glass  :  Nature 
and  Properties,  Manufacture.  Miscellaneous  Products.  Ap- 
pendix. Bibliography  of  Glass  Manufacture.  Index. 

This  volume  is  for  users  of  glass,  and  makes  no  claim  to  be  an  ade- 
quate guide  or  help  to  those  engaged  in  glass  manufacture  itself.  For 
this  reason  the  account  of  manufacturing  processes  has  been  kept 
as  non-technical  as  possible.  In  describing  each  process  the  object 
in  view  has  been  to  give  an  insight  into  the  rationale  of  each  step,  so 
far  as  it  is  known  or  understood,  from  the  point  of  view  of  principles 
and  methods  rather  than  as  mere  rule  of  thumb  description  of  manu- 
facturing manipulations.  The  processes  described  are,  with  the 
exception  of  those  described  as  obsolete,  to  the  author's  definite  know- 
ledge, in  commercial  use  at  the  present  time. 

Precious  Stones.  By  W.  GOODCHILD,  M.B.,  B.Ch.  With 
42  Illustrations.  With  a  Chapter  on  Artificial 
Stones*  By  ROBERT  DYKES. 

LIST  OF  CONTENTS  :  Introductory  and  Historical.  Genesis  of 
Precious  Stones.  Physical  Properties.  The  Cutting  and  Polish- 
ing of  Gems.  Imitation  Gems  and  the  Artificial  Production  of 
Precious  Stones.  The  Diamond.  Fluor  Spar  and  the  Forms  of 
Silica.  Corundum,  including  Ruby  and  Sapphire.  Spinel  and 
Chrysoberyl.  The  Carbonates  and  the  Felspars.  The  Pyroxene 
and  Amphibole  Groups.  Beryl,  Cordierite,  Lapis  Lazuli  and  the 
Garnets.  Olivine,  Topaz,  Tourmaline  and  other  Silicates.  Phos- 
phates, Sulphates,  and  Carbon  Compounds. 

An  admirable  guide  to  a  fascinating  subject. 

(  6  ) 


THE    "WESTMINSTER"    SERIES 

Patents,  Designs  and  Trade  Marks  :  The  Law 
and  Commercial  Usage.  By  KENNETH  R.  SWAN, 
B.A.  (Oxon.),  of  the  Inner  Temple,  Barrister-at-Law. 

CONTENTS  :  Table  of  Cases  Cited — Part  I. — Letters  Patent.  Intro- 
duction. General.  Historical.  I.,  II.,  III.  Invention,  Novelty, 
Subject  Matter,  and  Utility  the  Essentials  of  Patentable  Invention. 
IV.  Specification.  V.  Construction  of  Specification.  VI.  Who 
May  Apply  for  a  Patent.  VII.  Application  and  Grant.  VIII. 
Opposition.  IX.  Patent  Rights.  Legal  Value.  Commercial 
Value.  X.  Amendment.  XI.  Infringement  of  Patent.  XII. 
Action  for  Infringement.  XIII.  Action  to  Restrain  Threats. 
XIV.  Negotiation  of  Patents  by  Sale  and  Licence.  XV.  Limita- 
tions on  Patent  Right.  XVI.  Revocation.  XVII.  Prolonga- 
tion. XVIII.  Miscellaneous.  XIX.  Foreign  Patents.  XX. 
Foreign  Patent  Laws  :  United  States  of  America.  Germany. 
France.  Table  of  Cost,  etc.,  of  Foreign  Patents.  APPENDIX  A. — 
i.  Table  of  Forms  and  Fees.  2.  Cost  of  Obtaining  a  British 
Patent.  3.  Convention  Countries.  Part  II. — Copyright  in 
Design.  Introduction.  I.  Registrable  Designs.  II.  Registra- 
tion. III.  Marking.  IV.  Infringement.  APPENDIX  B. — i. 
Table  of  Forms  and  Fees.  2.  Classification  of  Goods.  Part 
III. — Trade  Marks.  Introduction.  I.  Meaning  of  Trade  Mark. 
II.  Qualification  for  Registration.  III.  Restrictions  on  Regis- 
tration. IV.  Registration.  V.  Effect  of  Registration.  VI. 
Miscellaneous.  APPENDIX  C. — Table  of  Forms  and  Fees.  INDICES. 
i.  Patents.  2.  Designs.  3.  Trade  Marks. 

This  is  the  first  book  on  the  subject  since  the  New  Patents  Act. 
Its  aim  is  not  only  to  present  the  existing  law  accurately  and  as  fully 
as  possible,  but  also  to  cast  it  in  a  form  readily  comprehensible  to  the 
layman  unfamiliar  with  legal  phraseology.  It  will  be  of  value  to  those 
engaged  in  trades  and  industries  where  a  knowledge  of  the  patenting 
of  inventions  and  the  registration  of  trade  marks  is  important.  Full 
information  is  given  regarding  patents  in  foreign  countries. 

The    Book ;   Its  History    and    Development.    By 

CYRIL  DAVENPORT,  V.D.,  F.S.A.     With   7   Plates    and 
126  Figures  in  the  text. 

LIST  OF  CONTENTS  :  Early  Records.  Rolls,  Books  and  Book 
bindings.  Paper.  Printing.  Illustrations.  Miscellanea. 
Leathers.  The  Ornamentation  of  Leather  Bookbindings  without 
Gold.  The  Ornamentation  of  Leather  Bookbindings  with  Gold, 
Bibliography.  Index. 

The  romance  of  the  Book  and  its  development  from  the  rude  inscrip- 
tions on  stone  to  the  magnificent  de  Luxe  tomes  of  to-day  have 
never  been  so  excellently  discoursed  upon  as  in  this  volume.  The 
history  of  the  Book  is  the  history  of  the  preservation  of  human  thought. 
This  work  should  be  in  the  possession  of  evey  book  lover. 

(  7  ) 


Van  Nostrand's  "Westminster"  Series 

LIST    OF    NEW   AND     FORTHCOMING 
VOLUMES. 

Timber.     By  J.  R.  BATERDEN,  A.M.LC.E. 

Steam  Engines.  ByJ.  T.  ROSSITER,  M.I.E.E., 
A.M.I.M.E. 

Electric  Lamps.     By  MAURICE  SOLOMON,  A.C.G.I., 

A.M.I.E.E. 

The  Railway  Locomotive.    By  VAUGHAN  PENDRED, 

M.I.Mech.E. 

Leather.     By  H.  GARNER  BENNETT. 

Pumps  and  Pumping  Machinery.      By  JAMES  W. 

ROSSITER,  A.M.I.M.E. 

Workshop  Practice.  By  Professor  G.  F.  CHAR- 
NOCK,  A.M.LC.E.,  M.I.M.E. 

Textiles  and  their  Manufacture.  By  ALDRED  BAR- 
KER, M.Sc. 

Gold  and  Precious  Metals.     By  THOMAS  K.  ROSE, 

D.Sc.,  of  the  Royal  Mint. 

Photography.  By  ALFRED  WATKINS,  Past  Presi- 
dent of  the  Photographic  Convention. 

Commercial  Paints  and  Painting.  By  A.  S.  JEN- 
NINGS, Hon.  Consulting  Examiner,  City  and  Guilds  of 
London  Institute. 

Ornamental    Window    Glass    Work.     By    A.    L. 

DUTHIE. 

Brewing  and  Distilling.     By  JAMES  GRANT,  F.C.S. 
Wood  Pulp  and  Its  Applications.     By  C.  F.  CROSS, 

E.  J.  BEVAN  and  R.  W.  SINDALL. 

The  Manufacture  of  Paper.     By  R.  W.  SINDALL. 

D.      VAN       NOSTRAND      COMPANY 

'Publishers     and     {Booksellers 
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University  of  California 

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